Dungeon Ecology: Making Your Dungeons Make Sense

Last Updated on January 22, 2023

Recently, I’ve found myself thinking more and more about dungeon ecology. 

The term originated in a long-running, popular series of articles in Dragon magazine that sought to take a more scientific approach to the monsters and magical creatures found throughout the world of D&D. 

Dungeon ecology is the idea that dungeons — not to mention other adventuring sites, towns, cities, entire worlds — in a game of D&D should function with some degree of internal logic that stands up to the scrutiny of the players. 

It deals with questions like “What are all these monsters eating?” “How do the goblins move around if their whole dungeon is full of traps?” and “How did they fit a dragon through that tiny door?”

In short, Dungeon Ecology is the practice of making your dungeons make sense. 

There are a few different schools of thought on how you go about answering those questions and what purpose answering them actually serves. 

To kick things off, I think it’s important to ask… 

Why Should I Care About Dungeon Ecology? 

In a game all about wizards and warlocks fighting giant, fire breathing lizards for their giant piles of magical swords, I think it’s completely valid to question why we need to care about making dungeons make sense. 

Take video games, for example. I don’t get annoyed when I walk into my fifth mob of enemies if I haven’t also seen where the bad guys cook their food and go to the toilet.

I don’t abandon a game because it doesn’t answer how a secret base halfway up a mountainside feeds the several thousand disposable goons every day. That’s not the point. 

If you don’t care about that stuff, then dungeon ecology probably doesn’t matter to you. But, hear me out. 

D&D ostensibly isn’t a video game, especially because it relies on a collective willing suspension of disbelief by people who play it.

My console isn’t about to stop rendering the next Moblin camp if I stop make-believing that Hyrule is a real place. 

If the immersion is broken in a game of D&D, however — if the world stops making enough sense for the players to see behind the emerald curtain — the story loses its power.

As dungeon masters, I think we have an implied duty to make the world of the game feel as real as possible or at least real enough so the players don’t feel the willingness to suspend their disbelief start to strain. 

I talk about this more in my article on creating Random Encounters, but essentially — more than plot and balanced encounters and background music — verisimilitude is our highest duty. 

Let me give you an example.

I was flicking through a copy of B2 The Keep on the Borderlands — one of the earliest and most enduringly iconic adventures written for the first edition of Dungeons & Dragons back in 1979 — and I saw something (in the titular keep, funnily enough, rather than in the Caves of Chaos – the actual “dungeon” part of that module) that made the idea click into place. 

Source: Jim Roslof, B2 The Keep on the Borderlands (1979), TSR/Wizards of the Coast

In the fabled Keep on the fabled Borderlands, there is a bank with a number of safety deposit boxes inside.

Because this is 1e D&D — and a large part of adventure writing back then was noting exactly how many gold, silver, and copper pieces every single farmer, bandit, and other sundry NPC had and where they’d hidden them on their property — the contents of the bank’s 12 safety deposit boxes are obviously listed for the DM. 

Two of them are trapped with poison gas or arrows by their paranoid owners (one of whom is the banker himself). Three of them are empty. And one of them contains four Pit Vipers. 

This struck me as weird. Why was one of the bank vaults in this medieval keep (which were otherwise full of gold, platinum bars, and alabaster statuettes) being used to store a nest of venomous snakes? 

Of course, I know why Gary Gygax, the game designer, put the vipers there.

In one of his games, the players decided to rob the bank, and he wanted to create some gameplay — something to remind the players that their actions have consequences — in the bank in case another group tried it. That’s all fine. 

What I don’t get — what stopped me short while reading the adventure and what I’m sure would stop my players short if they opened the vault and got mauled by a big angry snake — is why someone living in the Keep would pay to keep a bunch of pit vipers in the local bank. 

Are the safety deposit boxes airtight? If so, how do the snakes survive? If not, how certain is the banker that they won’t escape? Who feeds them and how often? 

Logical speed bumps like this aren’t uncommon in older modules.

They even crop up in modern adventures, especially when you get into lower levels of a big dungeon complex where, logically, food should be harder to find, but the monsters somehow keep on getting bigger and more numerous. 

Nine times out of 10, your players probably won’t notice — or they’ll just assume the adventure is playing by video-game rules.

No one writes off Raiders of the Lost Ark just because the movie glosses over how thousands of snakes survived for centuries in that one tomb. They’ll just rant about it angrily on Twitter 40 years later. 

It probably won’t destroy your game, but it might make it worse — make it feel like a cardboard filmLogical missteps like this probably won’t destroy your game, but they might make it worse.

They might make it feel more like a cardboard film set, a fake, a video game full of dummies arranged in a shooting gallery, and less like a living, breathing world.

Imagine. It’s the climax of the adventure. Battered and bloody, our heroes stride through the door to the dragon’s lair.

There, filling every inch of available space, the ancient black dragon Zargon the Despoiler sleeps — trails of noxious green smoke issuing from his nostrils. It’s time for a boss fight.

Source: Erol Otus, Dungeons & Dragons Basic Rules Boxed Set, TSR/Wizards of the Coast

Then, a player says excitedly, “Guys, it’s a fake! It’s not real. Look! We just walked through a normal sized door. The dragon’s huge. If this was a real dragon there would be a way for it to get in and out. See?!” Oops.

I’ve been thinking about dungeon ecology a lot lately. 

If you want to avoid embarrassing goofs like the now-infamous “Zargon Paradox” that my old group still gives me crap about or a mysterious bank vault full of snakes and just maybe make your games a whole lot better in the process, maybe you should be thinking about dungeon ecology too. 

How Do I Use Dungeon Ecology?

There are different ways that people go about approaching dungeon ecology. 

The first and older of the two I’m going to talk about is used interchangeably with an idea that’s become known as “Gygaxian Naturalism.” 

Dungeon Ecology and Gygaxian Naturalism

Dungeon ecology as a practice (in the sense that people were actively thinking about it rather than just, you know, doing it, man) took root in the Ecology series that ran for 30 years in Dragon Magazine, with many of its entries being penned by Ed Greenwood, the co-creator of the Forgotten Realms setting. 

The goal, starting with The Ecology of the Piercer in Issue #72, was to take a scientific approach to the fantastical beasts throughout D&D and treat them as any biologist would look at an animal in the real world.

Source: Dragon #72, Wizards of the Coast

Incidentally, the good folks over at r/dndbehindthescreen have worked on an amazing project to expand upon the Ecology series in a monstrously large tome detailing in extensive detail the ecological traits of pretty much every monster in the Monster Manual

The best part is: it’s free, right here.  

They examined everything from a monster’s feeding patterns, lifecycle, and internal organs to their impact on the local environment.

In short, they looked at dungeon denizens as though they were real animals and tried to figure out how that would affect the game. 

This approach came to be known as Gygaxian naturalism.

Eloquently described by James Maliszewski on the Grognardia blog: “The intention behind Gygaxian Naturalism is to paint a picture of a ‘real’ world, which is to say, a world that exists for reasons other than purely gaming ones.” 

Early D&D adventures made a more overt effort to note this stuff down than things I see written for 5e.

In Keep on the Borderlands, for example, Gygax notes all the numbers of non-combatant monsters (women, children, and old folk essentially) in the various orc, goblin, and hobgoblin tribes that populate the Caves of Chaos. 

That’s not to say that 5e content doesn’t do dungeon ecology. 

It very much does; I just think it’s become so ingrained in the design process that the writers assume that players are thinking about it too. 

One fantastic modern adventure that’s very much preoccupied with dungeon ecology is Out of the Abyss — hands down the best (okay, maybe second best; I have a huge soft spot for Night Below by Carl Sargent from 2e) Underdark adventure in D&D

That book pays huge attention to making the vast, sprawling nightmare that is the Underdark feel alive.

It considers the flora, the fauna, and how they fit together. It considers the logic of such a place, from the mushrooms that feed the insects all the way up the long and delicate food chain to humanoids and larger predators. It feels real. 

If the players in your game are the sort of people who notice this stuff, then having a book do the heavy lifting by answering questions like “what do people eat down here?” is hugely helpful. 

However, if you don’t run D&D for a gang of amateur botanists who like drawing energy pyramids, then the painstaking research you did into more than a dozen different species of fungus starts to feel like an awful lot of wasted effort that could have been spent planning an actual adventure. 

This is the big problem with being a Gygaxian Naturalist in the vein of the Ecology series.

Painstakingly applying natural rules that affect the real world to the creatures in D&D runs the very real risk of both making everything feel a good deal less magical and making the process of designing a dungeon that’s actually fun a good deal harder. 

It also doesn’t generate gamable content. 

However, the distinction between Gygaxian Naturalism and dungeon ecology more broadly is that, whether we’re talking about orcs, elves, or gelatinous cubes, Gygaxian Naturalism approaches all creatures and monsters in D&D as though they are actual animals. 

If that’s the sort of thing that floats your boat, then that’s fine. But — much like a 30-page document detailing the lore of your homebrew world — it serves us very little purpose at the table. 

This is where the second approach comes in. 

Dungeon Ecology as Theme

This approach jumped out at me while I was watching an excellent video by Map Crow. It’s a masterclass in how to use dungeon ecology as a way to support the adventure your players are currently on. 

Basically, dungeon ecology, according to this technique, is something to be applied to your dungeon’s gameable elements, rather than every passing blade of grass. 

It’s a way to help you narrow down your focus and think about how to express the story of a place and the creatures or factions that occupy it to your players when they walk inside. 

Used in this fashion, Dungeon Ecology actually becomes a tool that helps you write your adventures because it becomes a tool for expressing the dungeon’s Theme. 

If you have the central idea of your dungeon, which can be a monster, a magical artifact, a particular faction, etc., then the process of creating a dungeon ecology is just a matter of figuring out how that central theme affects the gameable elements of the dungeon – keeping in mind that gamable elements means obvious stuff like monsters, traps, room layouts, and less obvious things like the appearance and behavior of certain factions, and even the impact of the theme on the more Gygaxian Naturalistic elements of the local ecology. 

Let’s do a quick example in honor of everyone’s favorite inexplicably dangerous bankvault from The Keep on the Borderlands

The Snake Pit 

Let’s make a dungeon with a Giant Snake at the bottom of it. That’s the theme. Hey, no one said it had to be complicated or abstract.

This isn’t Tolstoy; we’re after two-to-three hours of good, clean investigation, exploration, and monster killing, not Anna Karenina.. 

We’re going to need to figure out: 

  • How/why did the snake get there? 
  • How does it survive? 
  • How does the rest of the dungeon express this theme? 

Answering each of these questions is going to take us from a very simple idea to something that’s approaching a fleshed-out dungeon or even a full adventure in no time. 

Let’s introduce a faction to explain why there’s a giant snake in a pit. 

How about a cult that worships it as a god? Sounds good. The cult built a giant underground pit and put a giant snake in it. Check. 

Now, snakes gotta eat. Maybe the members of the local cult are wealthy (which means they’re probably all important people in the local town or city, making them powerful enemies) and can afford to regularly buy pigs and cows to feed their serpentine deity. 

Either way, keeping a gigantic snake fed underneath, say, a small rural town, is going to have some knock-on effects. 

Maybe there’s not enough food for the local peasants and the snake.

Having the players walk into a village where the pigpens and pastures are filled with fat, happy animals ready for slaughter but the local peasants are all badly malnourished is a pretty creepy adventure hook. 

Maybe the food is running out. The livestock provides enough for the cultists, but maybe now the local peasants are the snake’s food. 

Already we’ve got an idea of how the presence of a single monster can ripple out to affect the whole local ecology in a gamable way.

All we need now is a dungeon map, a few other classic elements like a trap (what an excellent way to get peasants to throw themselves into the snakepit), and we’re good to go. 

As a very quick example of how this could be turned into a quick interlude adventure that you can use to challenge 1st- or 2nd-level players in your own campaign, let me present… 

Famine Above, Feast Below 

The village of Alder Hollow is dying, bled dry by the Serpent beneath. A snake cult has infiltrated this once-prosperous farming community. 

Promised great wealth and power by their new god, the prominent citizens of Alder Hollow have converted the crypts beneath the town’s church into a temple to The Serpent.

Beneath the town’s sleepy streets, they have allowed a monster to grow. 

Now, the people of Alder Hollow starve as the cult steals the town’s animals to feed the ever-growing Serpent. Soon, even the pigs and goats that remain will not be enough, so the cult is preparing to start using the local peasants for food. 

Will you save the people of Alder Hollow from the famine above? Or will you be cast into the Serpent Pit and become the next course in the feast below?

Hagra Constrictor
© Wizards of the Coast by Simon Dominic


Silas Selmen, The Mayor: Portly, licks his lips like he’s tasting the air. Hidden serpent tattoo under his collar. 

  • Wants: The adventurers to leave. There’s no famine here. 
  • Planning: To lure them into the temple to be fed to the Serpent. 

Esther Sherwynn, The Priest: Soft speech, punctuated by bright, harsh sibilants. Wears a brass snakehead ring set with an emerald and snakeskin boots. Sweating, like she’s just been in a sauna. 

  • Wants: To start feeding the peasants to the Serpent as soon as possible. 
  • Loves: The Serpent. 
  • Is: Really, really dumb. 

Thisselwod Hess, The Sherrif: Broad-chested, thick neck muscles like coiled snakes. Hisses to himself when he thinks no one is around. 

  • Has: A shed with just a few fat, juicy pigs awaiting sacrifice round the back of his house. 
  • Says: Poachers have been stealing the town’s pigs.
  • Wants: You to go steal them back and, if the pigs have been eaten already, to bring the bandits to him for “questioning.”  


Morgan, The Butcher: Thin, faraway expression, nervous. 

  • Knows: No one has any meat to sell him. 
  • Suspects: The Priest and the Mayor are stealing the pigs to sell in the next town over. 
  • Heard: A squeal like a pig in fright coming from the church last night. 

Tamra, The Farmer: Listless, with downcast eyes and dark circles under her eyes. 

  • Has: No pigs left. They were all stolen. 
  • Wants: Her pigs back. But the Sheriff doesn’t seem to care.
  • Saw: Hooded figures walking through the town at night. At least, she’s pretty sure she wasn’t dreaming. Probably. She’s been up looking for her goats for days. 

Elloren, The Poacher: Camped outside town, wary, hands always on her dagger. 

  • Thinks: Something fishy’s been going on. 
  • Says: She didn’t take those pigs. She’s being set up because she knows stuff, man.
  • Knows: Very little. Pretty sure the Mayor is a vampire pig. Pretty sure you’re all vampire pigs. Come closer, let me see your neck. 

The Serpent Pit

Maps made using Watabou’s One Page Dungeon Generator

Area 1. The Nave – Dark, velvet drapes over stained glass windows. Smells overwhelmingly of incense with something sweeter, fouler beneath it. Mural of Saint Innocuous, the patron saint of innocent, unremarkable people. 

Area 2. The Chapel – Vaulted ceiling. Shafts of light catching the dust. Dusty, disused altar with two burned down candles on it. Strangely warn and humid. Steam rising through cracks in the floor.

A trapdoor (unstable, 1-in-6 chance walking over it causes it to give way) in front of the altar opens by pulling a lever (untested, 3-in-6 chance it doesn’t work) to the left of the entrance, straight drop (2d8 Bludgeoning Damage; DC 12 Dexterity saving throw for half) into Area 6. 

Area 3. The Priest’s Quarters – Lavish velvet bedspread. Wardrobe containing basic priest vestments, and a luxurious black silk robe with a hood. Book of Psalms to Sain Innocuous on the desk.

The book’s insides have been hollowed out — now contains a scroll of Speak with Animals and a pamphlet titled “SHEDDING YOUR PAST SELFSKIN; WHAT THE GREAT SERPENT CAN DO FOR YOU!!” A black velvet curtain covers a flight of stairs leading down into Area 4. 

Area 4. Cult Hideout – Black candles, velvet drapery, clouds of incense. An altar covered in piles upon piles of massive snakeskins. Cursed Silver Statuette of the Serpent God with emeralds for eyes sits on the altar.

Worth 200 gp. Holding it forces a DC 10 Wisdom Saving Throw or become cursed. 

Curse of the Serpent: You must make a DC 10 Wisdom Saving Throw each time you eat to resist trying to swallow the food whole. The first time you meet someone, make a DC 8 Wisdom saving throw to resist the urge to hiss at them.

On a critical failure you try to bite them or crush them with your beautiful, serpentine body. You big, lovely, scaly boy, you. Hisss.

Area 5. Sauna – Braziers full of hot coals, like a sauna with a pail of water beside it. Stiflingly hot. Sound of something big moving to the north, scales on stone. A deeper hiss underneath the hissing of water on coals. The air smells of death and reptiles.

Used to keep the snake pit at optimum temperature. Door to Area 6 is barred from this side.

Area 6. The Serpent Pit – Pillars, darkness, oppressive heat. Bones crunch underfoot — small, perhaps animal, and larger.

A Giant Constrictor Snake waits here. There is a 1-in-6 chance the snake was fed recently and is sleeping. 

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