Dungeon Ecology

You all know the image (if you play tabletop RPGs, at least): a group of like four or five murderous weirdos descend into the chthonic depths of the earth in order to haul out chestfulls of gold (and maybe a princess here and there, too).

But, like, how do all these dank underground spaces GET there?

Who makes dungeons?

(from here)

I'm not really talking about literal dungeons - crappy little spaces with bars and chains to hold prisoners in some castle's basement. Those are usually pretty tiny, modest affairs, nothing like the labyrinthine, multi-level complexes of cave and tunnel that tabletop RPGs so often feature.

I ask who makes dungeons because they're so rare in real life. (Y'know, our actual world.) The reason for this is usually that it's dang hard to dig meandering tunnels and subterranean rooms through earth and rock. Dirt constantly wants to collapse on you (necessitating EXTENSIVE systems of support), and stone, in ADDITION to the danger of cave-ins, is simply a tough substance to break. And THEN you have to haul out all the material you create ALL THE WAY TO THE SURFACE (which, obviously, is farther away the bigger of an excavation you're creating).

All this explains why human-made underground spaces are so rare. In ancient and medieval times, really the only reasons to dig underground were 1) to make a stable foundation for large, expensive buildings, and 2) mining. (We STILL mostly follow these trends, by the way.) It's just not worth the effort to dig out any kind of structure underground, because it's always easier to build (and maintain) (and access) (and use) conventional aboveground buildings.

So, we're stuck with a convention in fantasy gaming that doesn't hold true in real life. (What a surprise.) We can do two things: toss out the convention and only create adventures in above-ground locations (and the occasional mine or basement) OR explain how dungeons still manage to arise in our gameworlds.

I've done the former fairly often, but in this post, I want to explore a possibility for the latter option!

Namely, trees. (And shrubs and weeds and shrooms and squirrels and other stuff that dies, decomposes and forms soil.)

Frekkin' TREES (from album artwork of Warforged - Essence of the Land)

Let me elaborate.

So, y'all know how dirt is made, right? It's mostly smashed-up rock (with particle sizes ranging from sand to clay) mixed with bits of dead stuff (mostly plants). This dead stuff we call "humus" (no, not "hummus," that gross stuff that stereotypical veg(etari)ans eat), and is really great for making fertile, arable soil rich in nutrients that plants need to grow (because it's mostly made of plants that DID grow there a while back).

Now, soil does build up over time as rock is weathered and plants die, but at slow rates that are often countered by erosion, compaction, or formation of sedimentary rock.

Now, since we're talking about FANTASY worlds, let's make it a bit more, well, fantastic.

Say, for instance, that in your gameworld, foliage (and maybe other forms of life, too) grow WAY faster than we're used to.

Like, we're talking about WAY faster than normal. Imagine ^this^ all over. (From the album artwork of Robert Rich - Somnium)

(You don't even need to put much effort into WHY this would be. Just wave your hand and intone something about "natural magic," "atmospheric composition," or (gods forbid) "druids.")

Fast-growing flora (and maybe fauna) would explain a lot of things. Here's a couple I thought of:
1) Why the gameworld is full of so much untamed wilderness - it just grows TOO FAST to keep most of it clear-cut!
2) Why acreage of farmland is so small compared to the gameworld population - crops grow fast and fruitful!
3) Why those infamously-large elf-infested trees get so huge!
4) Why monsters in the wild are so big!
5) Why the abundance of predatory species can possibly have enough prey to feed upon!
6) Why bandits are everywhere? (are they affected by the wild growthspeed, too?)
7) Why so many underground structures ("dungeons") exist!

Wait, what? Why 7)?

If there's a ton of plant matter constantly growing and dying, the buildup of soil will be SIGNIFICANTLY faster than we're used to. Maybe fast enough that abandoned buildings only a century (or so) old would be buried by fresh dirt.

DUNGEONS.

You see? Civilizations build towns, fortresses, keeps, halls, and whatever else - and if they are ravaged or abandoned, they are soon BURIED (and perhaps re-inhabited by the denizens of the subterranean world!) These tunnels you're walking through? They were once the hallways of a monastery. This cavernous room? Once the cupola of a temple's dome. This vertical shaft? Once the top of a well.

Certain features common among above-ground buildings would still be discernible, of course. Former windows allowing dirt and dense roots to poke in. Skylights, perhaps still open to the sky (even as the rest of the structure is buried). Former ceilings, buried, then collapsed, forming a cavernous space roofed only by roots and densely-packed soil.

Now, when your players ask you why there are all these well-cut, firmly-laid stone blocks in a massive underground complex that would've taken unimaginable efforts to dig and bolster, you can smile knowingly and start planting a clue every session or two. (A window to... dirt? A skylight with no sky? And, wait, how long ago did we plant this large tree? And, my, Fido has grown...)

In this gameworld, Civilization has a tomb of its own: the ever-grasping clutches of mighty Nature. (Album artwork from Halgrath - Out of Time)