The Underground Architect’s Dungeon Ecology

A Step-by-Step Guide to Creating

a Believable Dungeon Ecology

A frequent complaint people make about traditional Fantasy Tabletop Role-playing games is levelled at the Dungeon Crawl. They reasonably point out that the “Monster Condo” or Funhouse style of dungeon doesn’t seem real and immersive, or that it lacks coherence. They are quick to ask questions such as:

• How do the monsters live in one room in the dungeon?

• What do they eat? These are good questions, and there is a simple answer: They don’t live in just one room, as the doors in a dungeon open automatically for any passing monsters. They can come and go as they like, which is why these monsters show up on the Wandering Monster Tables (or at least they should!). The keyed monsters and wandering monsters eat other creatures that live in the dungeon. The dungeon is a complete ecosystem, just like the forest or swamp or what-have-you above it. This short guide will show you how to create a dungeon with a realistic and believable ecology in just a few simple steps. The process can even be used to improve an existing dungeon or adventure module.

STEP ONE - The Dungeon and the Wilderness are Connected

Which monsters inhabit the wilderness region around and above the dungeon? Make a list of them and decide where their lairs are. Some of those lairs should be above ground, some should be in the dungeon. You can assign the specific location later, in Step Five. Which large monsters or humanoid tribes are keyed to the dungeon? Make sure some of them are listed in the Wandering Monster Table for the surface areas.

STEP TWO - Food and Water Everyone already knows that the Wilderness is teeming with life. The various terrain types have lots of normal, small creatures like insects, rodents and birds. All of these creatures are food for other, larger creatures, and so on and so on, up the food chain to the biggest monsters. Your dungeon is inhabited in the very same way. The tunnels, caves, rooms and chambers are infested with slimes, fungi, insects and rodents. The slimes and fungi take sustenance from the air, stone, and water of the environment. The insects feed upon the fungi and slimes and are in turn consumed by still larger creatures.

• Ants • Beetles • Centipedes

• Crickets • Mice • Rats

• Spiders These “Dungeon Livestock” animals range in size from normal- to jumbo-sized, several inches long. These insects and rodents form the second link of the food chain.

Use these plants and animals in the descriptions of the locations and areas in your dungeon. Soon enough your players will not only expect to see various “dungeon dressing” plants and animals, but they will begin to assume their existence as a perfectly natural part of the environment.

Sample Ecology-building Description

The room is bare, cold, and damp. The walls are discolored with mold but still in good structural condition. Much of the floor is covered in a slimy

watery ooze which seeps from the walls, ceiling and floor. One 5’ wide passage leads out the center of one long wall (South). Many small (6” long) centipedes scurry about on the floor. There is a dead white snake, some 8 feet long, lying on the floor. Its body has been crushed in the center.

Notice in the description that “watery ooze that seeps from walls, ceiling and floor”. The underground areas are going to be wet. There is water everywhere in dungeons and caverns. Build this water into your descriptions, just like the small prey creatures. You can include small pools or puddles of water in low spots on the floor of rooms, chambers, caves and rivulets running along the hallways and tunnels. These are great opportunities for foreshadowing upcoming encounters or providing a chance for the party to encounter some more of the prey creatures, stopping for a drink at the puddle. Of course, they flee when the light hits them, possibly ratcheting up the fear and tension the party should already be feeling.

STEP THREE - Encounters are more than just Monsters These small creatures and fungi establish the existence of the food chain for larger creatures like mice, rats, snakes, lizards, etc. These “Dungeon Livestock” animals should seem perfectly natural to see or encounter in an underground setting. Likewise, the “Giant-sized” versions of these animals feed upon the smaller versions. These animals and “monsters” aren’t necessarily worth fighting, (though they may come in handy as a food source for the PCs in desperate straits, see below) so they do not necessarily need to be on the Wandering Monster Tables. They, and their sign, spoor and scat, should again be in the various descriptions of corridors, tunnels, rooms and caves.

You can mention them, or describe them, as perhaps fleeing from your party’s light sources, hiding in cracks or holes in the walls and floor.

Sample List of Dungeon Livestock

• Giant Amoebas

• Slime molds • Water molds

• Mushrooms • Toadstools • Puffballs

• Sac fungi • Fruiting bodies • Smuts

• Rusts • Lichens

• “Cave”-versions of ordinary animals o Cattle o Dog packs o Opossum o Sloth

• Fish

• Giant Insects and Spiders • Lizards • Rats

• Snakes

STEP FOUR - Wandering Monsters

One of the entries for a Common encounter on your Wandering Monster Table should be a sub-table of Dungeon Livestock for you to roll for/choose from, consisting of the Giant/Cave/Monstrous versions of all the types of creatures listed above. Sometimes these Livestock results can be described as live creatures that may or may not attack, or they may be encountered hunting, or eating other prey creatures. Other times the Livestock results can

2 Fruiting Body

1 Puffball

result in discovering a dead Livestock creature carcass, mostly eaten by something even larger, surrounded by footprints tracking through the blood, or dropped feathers/scales, or perhaps claw marks on the ground/walls. The connecting tunnels and corridors should frequently include descriptions of signs and spoor and scat of these larger Livestock animals and Wandering Monsters.

Sample Scene-setting Description

You make your way down the long, narrow corridor. The air is thick and damp and stifling. You can hear water dripping from the ceiling and running down the walls. Foul-smelling lumps of partially devoured carcasses covered in fruiting bodies line the tunnel, where the wall meets the floor. Or In the middle of the corridor, just at the edge of your torchlight, the discarded skin of a large snake curls on the flagstone. Pale, scavenging centipedes flee from your light, seeking cracks in the walls!

STEP FIVE - Lairs and Treasure

Now that you have created a food chain that is visible to your PCs implicitly and explicitly, you can finish

stocking the dungeon with the larger showcase monsters. Keep in mind each large monster should have access to the rest of the dungeon,

or at least enough of it to hunt and feed, and possibly a route to the surface, whether secret or concealed. Most of the larger monsters in the dungeon should also appear on the Wandering Monster Tables for the surface region above the dungeon (as described in Step One). This will be especially important for those Boss-type monsters and any humanoid monster tribes (which will likely number in the hundreds!). Humanoid tribes with underground lairs will always have two to three routes leading to other levels and at least one route to the surface.

A corollary complaint to the funhouse dungeon has to do with why these monsters have hoards of gold and silver coins. By creating a realistic ecology, you also create a realistic economy. The humanoid denizens of the dungeon may not have any need

for gold coins, instead using the horns, scales, or bones of their prey. In many cases these alternate currencies will be valuable in and of themselves, as spell components or as trade goods.

Sample alternate dungeon currencies and treasure Those hairy cave-cattle are good for yarn, cloth, and leather... Various parts or products of underground plants and animals are likewise valued by the denizens of the underground, not only as currency, but Trade Goods of a sort. Returning to the list of mundane plants and animals that constitute the food chain of the underworld, we can also determine alternative treasures and currencies:

• Slime molds – poisons, anesthetics, potion

components • Mushrooms – foodstuffs, drugs, dyes • Puffballs – traps and weapons, spell components,

delicate decorations or apparel

• Fruiting bodies – foodstuffs, poisons and dyes • Smuts & Rusts – poisons and dyes

• Lichens – foodstuffs and bandaging aids • Cave Cattle – yarn, cloth, horn, leather, meat • Cave Dogs – leather and meat, teeth for adornment

or currency • Cave Opossum – meat, leather, yarn and cloth • Cave Sloth – meat, leather, yarn, cloth, claws for

adornment or currency • Fish – meat, possible poisons, scales or fins as

adornment or currency

• Giant Insects and Spiders – crispy foodstuffs and poisons

• Lizards – leather, meat, and possible poisons

• Rats – meat and leather • Snakes – meat, leather, scales or fangs as adornment

or currency, venom

FORAGING IN THE DARKNESS Adventuring parties run the risk of shortages while delving deep into the earth, where consumable resources such as light, water and food are essential to survival. Once per Watch (four-hour period) a PC may declare that they are spending the entire Watch Foraging. Any PC can do this, though some classes and backgrounds may be more successful that others (per your individual campaign setting). Roll a d12 once per day for being able to hunt/gather some food to supplement any rations. In the absence of any rations, this activity can replace them. A result of 1-3 on the die indicates success in finding sufficient edible fungi, insects and/or rodents for four

man-sized creatures to survive for one day. A result of 4 on the die indicates enough food was found, but some has been mis-identified, and may cause a form of food poisoning. Each PC must save vs Poison or become incapacitated for 2d8+8 hours, as they are wracked by cramps, vomiting and other terrible symptoms.

SAMPLE ENCOUNTER TABLES Table 1 Surface Encounters, 2d6

2 Rare, Large Surface monster - Table 1.1

3 Rare, Large Dungeon Monster - Table 1.2 4 Humanoid Surface Tribe, Hunting party

5-6 Patrol, Human

7 Common Wilderness Animals 8 Unc. Surface/Dungeon Monster - Table 1.4

9 Uncommon Surface Monster

10 Humanoid Dungeon Tribe, Slaving Party 11 Rare, Large Dungeon Monster – Table 1.2

12 Boss-type Dungeon Monster - Table 1.5

Table 2 Dungeon Encounters, 2d6

2 Rare, Large Surface monster - Table 1.1

3 Rare, Large Dungeon Monster - Table 1.2 4 Humanoid Surface Tribe, Hunting party

5-6 Patrol, Dungeon Humanoid

7 Dungeon Livestock – Table 1.3 8 Uncommon Dungeon Monster - Table 1.4

9 Uncommon Surface Monster

10 Humanoid Dungeon Tribe, Slaving Party 11 Rare, Large Dungeon Monster – Table 1.2

12 Boss-type Dungeon Monster - Table 1.5

Table 1.1 Large Surface Monsters, 2d4

2 Rare

3 Uncommon 4 Common, Sign or Track

5 Common

6 Common 7 Uncommon

8 Rare

Table 1.2 Large Dungeon Monsters, 2d4

2 Rare

3 Uncommon 4 Common, Sign or Track

5 Common

6 Common 7 Uncommon

8 Rare

Table 1.3 Dungeon Livestock, 2d4

2 Cave Sloth 3 Giant Insects/Spiders

4 Snake

5 Centipedes 6 Lizard

7 Rats

8 Cave Cattle

Table 1.4 Uncommon Surface/Dungeon Monster, 2d6

2 3

4

5 6

7

8 9

10

11 12

Table 1.5 - Boss-type Dungeon Monster, 1d4 1

2

3 4

Fill in the above tables with the monsters and animals appropriate to the terrain in your setting.

SUMMARY The addition of a few small details can add much to the immersion of a dungeon scene. For most underground areas in each region these details are likely to be very similar. It is recommended that you customize and tailor each set of Wandering Monster Tables to the geography and terrain of the surface to make the dungeon distinctive.

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Words and Cover Cartography by Stephen Smith ©2021

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