Tag Archives: underworld

Missing Manuals

Every once in a while, but with some regularity, someone will ask for module recommendations, often as a way to get into old school or classic play. I am somewhat conflicted regarding the best response to such requests because, while there is nothing fundamentally wrong with modules, and they have some particular utility, modules are also limiting, often have poor handling, and are poor examples of the form’s potential.

My inclination is to instead suggest that referees, even new referees, create a simple custom scenario. This is unnecessarily intimidating, partly due to some unfortunate ingrained assumptions, including seemingly upward comparison to professional offerings with illustrations, cartography, edited prose, and so forth. In reality, crafting a satisfying classic scenario is often less complicated than the process of building a player character in a contemporary system, but has become obscured by a shroud of world building complexity and the detritus of expectations related to literary story structure. There are a few examples of procedures that a referee can follow to create a scenario, such as Moldvay’s double spread in 1981 Basic D&D (pp. B51-B54) which explains how to create an adventure. The recent Old School Essentials SRD provides similar information, available for free online (adventure scenarios, designing a dungeon, designing a wilderness). Other resources exist as well, though often buried in other materials.

These resource are useful, but still often seem to be pitched at the wrong level, lacking sufficiently concrete set of recommended actions, or attached to bland thematic content. As an example of the kind of referee rules that I think would be an antidote to module recommendations, I want to highlight two recent blog posts about crafting megadungeons:

The Two Week post in particular is a practical and clear example, though perhaps still slightly intimidating for a starting referee. Unfortunately, the trappings of a megadungeon is probably mildly counterproductive, despite the likely truth that following Nick’s megadungeon building guidelines would probably be easier and more enjoyable than skimming B2, or just about any published module scenario. (In reality, the observant and experienced reader will also note that a megadungeon is really just a series of linked scenarios that happen to be subterranean.)

If you are aware of any other similar scenario building procedures worth highlighting, drop them in the comments. Procedural rules rather than something like a collection of tables would be most useful. I am sure I am neglecting some other good resources. This is also a call for what to include in a game’s referee book or section.

Zines for megadungeons

(Being a review of Megadungeon #1, among other things.)

Since rediscovering fantasy roleplaying games sometime around 2011, I have followed the development of several home brew megadungeons. Some of my favorites include the taking-OD&D-seriously Dwimmermount, the Lovecraft-by-way-of-Vikings Black City, the Diablo-infused “precious shithole hellscape” Nightwick Abbey, the steam-age demonic fantasy cruise-ship-as-megadungeon HMS Apollyon, and the gleeful toybox-filled deity-haunted dungeon Numenhalla. These projects remain mostly unpublished1, present only as referee-musings, map-fragments, or, travelogue-style, as scattered session reports.

Numenhalla, however, is finally seeing (gradual) publication in the recent Hack & Slash zine Megadungeon, of which two issues are available as of this writing. This post considers Megadungeon #1, which contains a mix of referee advice, setting glimpses, some player-facing rules, and a couple intro dungeon areas. First, I will cover what I consider weaknesses, along with a few observations. Then, I will cover strengths and the promise Megadungeon (the zine) has for the practice of developing megadungeons for play.

The presentation has several weaknesses, the primary being transitions. Many of the sections began life as a blog posts, and it shows. This is only a minor flaw; in some ways, it even adds to the utility, creating a series of self-contained easy to reference nuggets, but it also makes the whole feel more like a grab bag than a carefully designed book. The amount of actual dungeon content in this issue is also rather small. While the two dungeon areas are wonderfully evocative, with beautifully hand-illustrated maps, they are also somewhat linear and detail only 15 keyed areas (dungeon content arguably occupies 5 of the 38-some zine pages). While I think it is a common mistake to attempt keying a giant sprawl of rooms when starting a megadungeon, rather than working with a more tractable map, I was still hoping for a bit more. That said, the creativity of the areas makes up somewhat for the quantity, and I realize that issue one also may involve more setting and play advice groundwork compared to future issues.

Crop from page 8

The biggest strength, apart from the obvious enthusiasm, is the art, which projects a sense of playfulness that is too often lacking in fantasy art. However, the playfulness never descends into explicit goofiness or self-deprecation, and at some points almost verges into a sense of the mystic (a good thing when attempting to capture the fantastic). The dungeon features themselves are often weighted with promise (see the pitch black door, for example). I have less to say about the various rules bits, such as the augatic class (a tin man style robot that gains new powers through upgrades), but they are well done and easy enough to drop into any game using a B/X type engine.

Though the last handful of years has produced several notable published megadungeons2, such as Stonehell, Barrowmaze, Castle Gargantua, and Maze of the Blue Medusa, I would still like to see more experimentation in different ways to present a megadungeon for direct use by someone that is not the dungeon’s author. To my knowledge, no existing megadungeon has used a zine format so I am curious to see where Courtney takes this. The closest approach I am aware of is the collaborative darkness beneath megadungeon published in the now-defunct Fight On!. Though there were a few standout levels, such as Sham’s level 2 and level 3, it suffered overall from a lack of coherent vision.

The zine format encourages zone-level publication, which naturally breaks down the task into more achievable units. While this might be less of a concern for Numenhalla, as I gather a large portion of the dungeon is already designed, it would probably be a good approach for any referee who wants to share their megadungeon. The major challenge using this form is that a good dungeon contains relationships between various areas, and this is difficult to pull off if one creates and publishes areas in sequences. How does one include a well-considered gate to level 5 in level 1 if level 5 is as yet undefined? Notably, the Numenhalla entrance halls do contain several (locked) connections to deeper areas, but we will need to wait for future issues to see if the dungeon can make good on this promise. 

Anyone interested in the idea of megadungeon play would probably get something out of this zine. As the text states:

Numenhalla lies beneath all cities,
All mounts and valleys,
And all lands.

As a disclaimer, I have gamed with Courtney both as player and referee.

Purchase info

  • Date: 2017-12-19
  • Price: $12.85 + $1.16 (local tax) + $5.32 (shipping) = $19.33 CAD
  • Details: RPGNow print on demand + PDF

See here for my approach to reviews and why I share this purchase info.

1. The ACKS-published extrapolation of Dwimmermount is the closest to publication for any of these dungeons, but ultimately completes a different project than the original idea behind Dwimmermount.

2. I make no attempt here to offer a comprehensive list of recent megadungeons, but the ones I listed stand out as attempts to push the form in various ways.

Scavenge Dungeon Move

The playbooks inspired by Dark Souls that I am developing for my current Stonehell game do not include traditional attack bonuses derived from class and level. Ability bonuses do contribute to attack competence, and ability scores do improve with advancement, but the scope of bonuses is the stingy B/X +0 to +3. To fill the game role of the attack bonus, Adventurers may enchant weapons. I envision a mechanism similar to that of Dark Souls, where players gather item drops such as titanite shards from monsters and then pay smiths to improve weapons using those resources.

Scavenging and Moves

To gather Monster Parts as resources for later use, Adventurers can use the Scavenge Dungeon Move if there are monster remains available (such as following successful combat). In the Hazard System, Adventurers take Dungeon Turns to make Dungeon Moves. Some example defined moves are Climb, Explore, and Search. This is similar to the various traditional D&D X in 6 checks, though more formalized. In practice, players often need not declare Moves explicitly (though they can), but, for example, the referee will naturally interpret moving from one dungeon area to another as the Explore Move and call for a Hazard Die throw. Making Scavenge a Move means that players expend dungeon time in exchange for weapon improvement resources.

Monster Parts as Incentives

Such resources also provide an incentive to engage monsters, though not necessarily directly. Since one can scavenge the corpse of a trapped monster killed from afar just as easily as one slain in a fair fight, and with less risk, players are rewarded for clever stratagems. Hunting monsters for parts also requires taking care to not damage the goods in the process. Unlike in traditional D&D, in my games Adventurers do not get any XP for blasting an enemy to smithereens with a fireball. This incentivizes player creativity much like rewarding experience points for treasure spent, though the best strategies may differ. (I am also rewarding XP for treasure spent.)

Monster Parts and Improving Weapons

Monster Parts can lend additional properties to weapons, such as fire enchantment from fire monsters. Improvise Monster Parts properties using common sense. There is no need to preemptively design a complicated taxonomy. For example, assuming traditional monsters, Monster Parts Scavenged from giant centipedes might be Poison Monster Parts. To increase the difficulty of improving weapons, have only uncommon or rare monster corpses supply useful Monster Parts. I think allowing brutal weapons or creepy upgraded weapons to be built out of common orc or skeleton parts could be fun though. I generally prefer to make just about all possibilities open to low-level characters so I plan to follow the second route (making all monsters provide Monster Parts).

For simplicity, do not differentiate between monsters with regard to quantity of Monster Parts available. One Adventurer Scavenges Monster Parts from one monster with one Dungeon Move and that exhausts the monster carcass. Specific or unique monsters may be exceptions to this rule. Six parts per Gear Slot seems like a reasonable default for encumbrance, though this is also something that can easily be adjusted by situational ruling. Maybe dragon Monster Parts take up a full slot per part.

Determining Degree of Scavenge Success

I am planning initially to make Scavenge success depend on a Wisdom Check. Make the check, gain 2 Monster Parts. Fail, gain 1 Monster Part. Critically succeed, gain 3 Monster Parts. Critically fail, spoil the remains. A critical success is the best result from the d20 or success by four or more.This follows my general approach for d20 partial success, based on the OD&D purple worm swallow mechanic. In shorthand, gain degree of success +1 Monster Parts.

Alternatively, substitute some system other than a Wisdom Check to determine Scavenging effectiveness, or just grant a unit of Monster Parts for spending a turn and enduring the roll of the Hazard Die. A simple d6 roll would work, avoiding the influence of ability scores, as would an Apocalypse Engine 2d6 roll with success thresholds at 7+ and 10+. Time passing and resource attrition are the important trade-offs.

Since enchanted weapons are powered by the Adventurer’s soul, improving weapons early in the game need not flood the fictional world with glowing +1 swords.

How many Monster Parts are required to upgrade a weapon and how much does it cost? That seems like a topic for another post and will probably require some experimentation and adjustment during play testing. This post has gone long enough. To end, have a formal rule in the Hazard System style.

Dungeon Move: Scavenge

To Scavenge the corpse of a defeated monster, make a Wisdom Check, scavenging Monster Parts equal to the degree of success + 1. Note any special Monster Parts properties, such as poison, slime, or fire.

Stonehell: Prepare to Die


  • Use a chassis similar to B/X
  • Use a published dungeon and structure the setting around the dungeon
  • Reinterpret dungeon elements using a Dark Souls filter


On the frontier of the central kingdom, the High King Vollrath built a fortress in the mouth of a dusty box canyon. Though billed as a borderlands fort, the location was not strategic. The extensive excavation and heavily loaded provisioning caravans were out of all proportion with a mundane outpost. After completion, visitors slowed and then stopped. One day the gates closed and did not reopen. For months, lights and guards were still visible on the parapets, and then those too vanished. Years passed, and parts of the wall fell into disrepair. Nature began the gradual process of repossessing the edifice. Then, the High King was defeated in battle and unified kingdoms fragmented again. Locals assumed that the distant civilized Central Kingdoms had forgotten the fortress.

A generation ago, those dwelling near the fortress began to behave strangely, gripped by unnatural passions. Many had nightmares. People regularly had bouts of uncontrollable rage or crippling fear. Settlers abandoned homesteads, soldiers sent to garrison outposts deserted, and trading outposts gradually became ghost towns. Soon, industry ceased.

Most people that linger are mad or catatonic, though a few have managed to retain their selves. Even the sane are plagued by nightmares with uncomfortably similar details: dark tunnels, shriveled men scurrying on all fours like roaches, and glittering treasures. Drawn by rumors of wealth, some fortune hunters regularly trek from the now divided Central Kingdoms, assuming the dangers superstition. None enter the nearby frontiers without being changed. Even those not driven mad suffer tremors and strange uncontrollable emotions that intensify with distance from the complex, growing into an obsession with the abandoned fortress. Until they return, colors are dimmer, food tastes like dust, and nothing seems to satisfy. All return, many to die in the depths or to a madman’s cracked blade.

Next up: B/X style playbook design inspired by Dark Souls starting classes.


St. Sebastian with lantern (source)

St. Sebastian with lantern (source)

Torchbearer has many rules that I think could profitably be spliced into more traditional dungeon crawling games. Of these, light coverage is perhaps one of the easiest to apply. Light coverage is the idea that the amount of illumination provided by a given light source is limited. Rather than trying to measure this using a literal approach of light radii as is commonly done in D&D, Torchbearer measures illumination by the number of characters that can benefit from a given light source (1 for candles, 2 for torches, and 3 for lanterns).

In addition to the number of characters fully covered by a source of illumination, a similar number of characters are in dim light. For example, a party of seven adventurers with one torch would have three characters in full light, three characters in dim light, and one character in darkness. Both dim light and darkness are factors in Torchbearer tests, which could easily be modeled as situational penalties in other games. The exact numbers here do not really matter, and could be adjusted to reflect however various light sources are conceptualized.

While considering how to handle grenades or other area affect attacks within a monologic combat framework*, Gus suggested that perhaps various area affect attacks, such as grenades or fireballs, could have an explosion rating indicating the maximum number of enemies that could be affected. I immediately thought of light coverage. Splash or blast damage, like movement distances, are hard to resolve satisfactorily and without handwaving when using fictional positioning. In the past, I have thought of area affect

The coverage rating would reflect the most targets that could potentially be affected by a given effect or item. The referee would still need to make a ruling about whether or not this coverage capacity was “filled up,” but the coverage rating would provide convenient and easy to understand guidelines, along with an upper bound. A second tier of effects, similar to how Torchbearer handles dim light, could be used to model something like secondary splash damage from a molotov cocktail. Coverage ratings could also be used for weapons such as nets, or even potentially special attacks using more conventional weapons (two-handed sword sweeps and missile volleys come to mind).

I suspect this general coverage approach could also be applied to abstracting other rules that are difficult to get a clear shared geometric understanding about.

* See: monologic combat.

OD&D dungeon monsters

Pages 10 and 11 of The Underworld & Wilderness Adventures (OD&D book three) contain tables for the determination of wandering monsters in the dungeon, one for each dungeon level, down to level six. These tables have eight to twelve entries each. In addition to containing information about implied setting, this collection of monsters functions in a certain way with other rules elsewhere in the game. While OD&D is robust enough to work just fine if other monsters are used, these linkages, and the roles that these monsters serve, are still interesting to consider.

Special monster attacks and defenses interact with equipment and character abilities. Monster defenses require special weapons to overcome. Silver weapons are required to damage lycanthropes, magic weapons are needed to combat gargoyles and many kinds of undead, acid or fire is needed to fully destroy trolls. Monster attacks can be resisted by certain defenses or cured by particular resources. The antidote to poison is the fourth-level cleric spell neutralize poison, petrification can be fixed by the sixth-level magic-user spell stone to flesh, elves are useful for resisting ghoul paralysis, mummy disease (which impairs recovery) can be handled with cure disease, basilisk gaze attacks can be reflected with mirrors, scrolls of protection are useful against entire monster groupings. And so forth.

Another pattern to note is that most levels draw monsters from the same set of categories, though not all levels have examples of monsters from every category. For example, magic-users only show up on levels two and deeper, and giant animals only appear on the first four levels. All the monsters in a particular category may not just be palette-swapped, but they do tend to broadly share qualities such as types of attack and vulnerabilities. The most common wandering monster categories seem to be: fighters, magic-users, undead, humanoids, giant animals, dragon types (though only on the deepest two levels). This is important because these categories communicate threat information to players that can be used profitably against more powerful variants of the same monster type.

The content triumvirate of monsters, equipment, and spells work together as a set of interconnected, opposing relationships. Monsters have strengths and weaknesses, which can be defended against, or exploited by, the tools available to players, which include those aforementioned categories. Replacing these elements with new, custom content is a common method of constructing a unique and surprising campaign setting. By no means do I wish to suggest that this is inadvisable. It may even be necessary to engage or challenge experienced players. However, it is probably worth considering these game mechanical relationships and making sure that similar dynamics exist within new collections of monsters as well, rather than making every creature entirely unique and unpredictable.

See also, regarding interactions between game constructs:

Torchbearer grind record

In Torchbearer, on every fourth turn candles go out and PCs gain a condition, on every third turn lanterns go out, and on every second turn torches go out. (Conditions are things like hungry, angry, and dead.) This is called the grind. I found that I wanted a nice record sheet that had this stuff on it, so that I could mark turns as they passed and know what was happening without needing to think about whether the turn was divisible by two, three, or four (and also because a record is nice to have).

So I made a grind record sheet, and here it is.

(The image below is kind of low-res, but if you click on it, you will get a PDF.)

Necropraxis Torchbearer grind record

Necropraxis Torchbearer grind record

Marching order and roles

Chaos party with marching order roles

Chaos party with marching order roles

Establishing a marching order in a videoconference game is a hassle. It always seems to take longer than it should, and then PCs in the middle or back are doing things which should often disturb the previous marching order, but practically speaking it’s just difficult to keep everything in mind along with everything else going on, such as describing the area, mapping on Twiddla, or checking off the passage of time.

Dungeon World has a formalized system for wilderness exploration which requires characters to take on different roles, the Undertake a Perilous Journey move. Specifically, characters can take on the trailblazer, scout, and quartermaster roles, which, respectively, improve speed, decrease the chance of being surprised, and decrease the number of rations consumed during the journey. Each PC that takes on one of those jobs makes the equivalent of a wisdom check (roll +WIS in DW parlance), and the result of that roll contributes to their given job.

A similar system could perhaps be used for abstracting marching order. Rather than worrying about exact order, just assign the key positions. Roles that I can think of are:

  • Scout: Assumed to travel beyond the light source, and report back periodically. Using a scout guarantees that the party will not be surprised from the front by visible dangers, though the scout risks being surprised.
  • Vanguard: protects the center of the group from melee. Up to two may take the vanguard role given 10′ hallways.
  • Second rank: may attack with reach weapons if the vanguard is in melee.
  • Torchbearer: you might want to double up on this role, as the light source is an obvious target for the minions of darkness.
  • Rearguard: function like the vanguard if the group is approached from behind.

So, rather than “give me a marching order,” instead: “who is scouting? who is vanguard?” And so forth. The actual order is not so important as long as the roles are filled. These roles can also carry some weight in more open spaces. For example, the vanguard could be assumed to intercept incoming melee combatants first, followed by the second rank, etc. PCs could of course override these default positions at any point, but I think a shared understanding about these roles might make abstract combat flow more smoothly, especially in games played over Google hangouts or similar technology.

I am also planning on including fields for these roles on my session record sheet. Such spaces could also double as session attendance (useful for things like handling treasure awards later).


Barrowmaze II; poster was a crowd-funding backer perk

Being a review of volumes 1 & 2 of the Barrowmaze megadungeon, written by Greg Gillespie (who blogs at Discourse & Dragons). The points in this review generally apply to both volumes unless specified otherwise.

The core idea behind Barrowmaze is a dungeon of tombs spread out beneath a collection of burial mounds. Rather than extending vertically underground like most megadungeons, BM extends horizontally, with difficulty varying as progress is made across the map. Being based on tombs, undead are heavily represented, but they are by no means the only foes that adventurers will come across. There are also several factions of other creatures struggling for control of the Barrowmaze underworld. Overall, the concept is very strong, and the numerous tricks and traps, along with plenty of new monsters, keep the dungeon feeling new and fresh throughout.

I will say right off that, despite a few usability issues, this is one of my favorite dungeons to date, and certainly one of the strongest OSR efforts. It sings with Greg’s direct voice and vision. This is not just a module, but also a treatise on how to run a traditional megadungeon, with emphasis on the risk/reward trade-off. For example, examining burial alcoves, breaking bricked-up walls, and general searching all come at the cost of random encounter checks. This is of course true in all traditional dungeon play, but is made extra salient by the numerous systems that Barrowmaze incorporates, such as using sledge hammers to break door slabs and masonry.

Image from Discourse & Dragons blog

Greg went all out regarding the art, especially in volume 2 (which benefitted from crowd-funding financing), and the illustrations are uniformly fantastic. The Holloway picture of the mummy on the back cover of BM 2 is especially noteworthy, but the interior black and white illustrations are also quite strong, and communicate the atmosphere well. There are approximately 60 monster write-ups, and every single one has a picture. Add to this the illustration booklets (for showing to players) that were added for both volumes during the crowd-funding campaign for volume 2. The layout is also crisp and professional looking throughout, and a consistent use of bold and italic makes mechanical info easy to pick out within room descriptions. Personally, I would like it if clues were also highlighted in some way, but I have yet to see a published module that does something like that.

In addition to the small overland area containing barrow mounds, the dungeon proper, and all the new game content (magic items, spells, monsters, etc), Barrowmaze also contains several useful random tables for things like thematically appropriate dungeon dressing and dungeon graffiti. Some of these tables are duplicated between both volumes (a spot check makes the dungeon dressing table in both volumes seem identical between BM 1 and BM 2, but a few of the other tables have minor modifications). BM 2 includes a totally new sarcophagus contents table.

My favorite part of Barrowmaze II is actually a random barrow mound generator. This is a tool (with helpful worksheet!) that allows you to quickly roll up a barrow-themed mini-dungeon by stringing together a (random number) of tomb chambers with varying things like door type, other features, traps, and grave goods. I have already profitably used this generator in a number of places, and it can easily be re-skinned for use in generating other types of areas. The worksheet format in particular is perhaps a model for other similar multi-table tools (it might work well for something like the Random Esoteric Creature Generator, or a random demon generator).

My copy of the first printing of BM 1

However, I do have two criticisms, one large and one small. The large criticism applies to both volumes. The problem is that the map of the Barrowmaze dungeon proper is split seemingly with regard only to page boundaries (not dungeon zones) and included at the end of the book, making referencing the map when reading the room descriptions inconvenient. Rooms, and sometimes even room numbers, are sometimes cut in half based on how the map was paginated (examples: rooms 248 and 265). If one only had the printed book, this would be awkward to use. A separate high-res PDF map file is available, but it is not included with the main PDF and must be purchased separately.

The cartography and layout of the barrow mounds section is much more successful. The mound maps are mostly on the same page as their keys, making them easy to run out of the book. The rest of the dungeon would be much easier to use if it were presented similarly, in dungeon zones or zone fragments.

The small criticism applies only to Barrowmaze 1. That book is around 75 letter-sized pages worth of content. Of that, 12 pages are dedicated to pregenerated characters on full character sheets, one per page. I do not think this is an effective use of space. Barrowmaze 2 is much better in this regard, presenting the same amount of pre-gen content in only 4 pages, and with much better art.

On balance, my recommendation is high. You will likely need to do some prep with the maps before running Barrowmaze, but some level of prep is required with all modules. As a craft, module writing is actually still at a relatively early stage, I believe, and work with efficient form factors is ongoing. The area descriptions, however, are quite good in terms of their level of detail and usability. Most are short paragraphs, with concise text and relationships to other areas clearly presented, and the various tricks and monsters are creatively laid out and easy to get a handle on. Barrowmaze would make an excellent companion for something like an all-in-one starting Labyrinth Lord campaign.

One final note: it looks like Barrowmaze is going on sale this week.

Caryatid Columns, Barrowmaze II page 32

The Symbiotic Dungeon

The classic D&D setup is a town or city with a dungeon nearby. Assume for a moment that the dungeon’s proximity to the town is not coincidence. From the point of view of the townsfolk, situating their town in this way does not seem like a wise move. People generally build settlements near resources (mines, farmland) or transportation routes (rivers, passes, roads).

In a traditional game, the dungeon resource is treasure, but treasure is almost by definition, a luxury. It is not something that yields any return outside of exchange society. Treasure is, after all, inherently almost valueless. The value of money (gold included) is a social construct. There are many other useful things that might come out of a dungeon though. Here are a few of them. If the setting is truly dangerous, such as a post-apocalyptic wasteland, or demon-infested wilderness, controlling a dungeon entrance might even be the only way any kind of civilization might be able to survive (for an extreme example, consider ancient domed cities on mars which require archaic fuel cells to power the life support systems).

Dungeon Bounty
  1. Ancient fuel cells (required to power technology or weapons)
  2. Rare magic components
  3. Wandering souls on their way to the underworld (mechanic for resurrection?)
  4. Gastronomic delicacy or rare spice
  5. Sole source of potable water (surface water is polluted, poison, or intoxicating)
  6. Slaves (goblins taken from the underworld make up an underclass like helots)

There is a danger of starting out too weird, and scaring off or confusing your players. If you follow such threads to their logical conclusions, you may end up with a society based on dungeon ecology which is totally unrecognizable. You probably don’t want to begin your campaign with a 10 page setting document for your players to read. As James Raggi suggests though, there is no need to go overboard with explanation and backstory. Even to yourself, as who knows where your ideas (and the dice) might take you in the future? Also, there is no reason why the level one PCs should know how things actually work. Let the characters discover things slowly, starting from a relatively mundane and recognizable medieval setting (with, in the tradition of good speculative fiction, one or two aspects varied).

Alternatively: dungeons are so dangerous that once discovered they must be sealed and guarded, lest their denizens overwhelm the surroundings (remember the turnstiles and holy water hoses of Blackmoor in The First Fantasy Campaign). Perhaps dungeon entrances are gates to hell, the no-man’s land in the never ending war between cosmic factions. This is not incompatible with the conception of the dungeon as mythic underworld. Rewards will be given by the authorities to those brave enough to enter and help subdue the demons. Entrance to the dungeon without permit is harshly punished, and secret entrances are highly prized by adventurers (though they also risk allowing the dungeon’s evil to leak out). The penalty for entering a dungeon without permit is death.

This evil could also be considered a bounty, by those imprudent and power-hungry. A dark magician, or evil high priest may try to ally with the denizens of the dungeon in order to harness the power of the underworld to subdue neighbouring lands.