Location from The Gods are Bastards by D.D. Webb
A sentient dungeon beneath Last Rock University — an ancient, self-aware labyrinth that rearranges itself, generates monsters, and has been trading with adventurers for longer than most civilizations have existed.
The Crawl is alive, and it is very, very old. It's a dungeon in the classic sense — a labyrinth of challenges, treasures, and monsters — but it's also a sentient entity that has developed something like a personality over millennia. It creates challenges calibrated to the adventurers entering it, generates ecological systems that shouldn't exist, and maintains an economy with the surface through the upper-level markets. It's not hostile by default — it's more like a vast, alien intelligence that finds the interactions between itself and mortals interesting. The relationship between the Crawl and the University is symbiotic: the University uses it as a training ground, and the Crawl gets a steady supply of interesting visitors. The deeper levels are genuinely dangerous. Adventurers have died in the Crawl. It doesn't apologize for this — death is part of the ecosystem it maintains. The bottom has never been reached, and there are theories about what's down there that range from treasure to trapped Elder Gods.
Descending levels carved from living rock, shifting and rearranging between visits. The upper levels are almost civilized — a market area, an inn called the Grim Visage, and relatively safe corridors used for training. Deeper levels become increasingly alien: bioluminescent growth on walls, architecture that doesn't follow euclidean geometry, and an oppressive sense of being watched by something vast and patient. The air gets warmer and wetter as you descend.
Also known as: The Crawl, The Descent, The Dungeon