The
Danmachi franchise of light novels and anime features a dungeon that is a single, malevolent (or justifiably angry, take your pick) living organism that happens to produce invaluable magical resources. Most monsters are generated spontaneously on the spot as a sort of antibodies against the invading adventurers. The monsters that survive the encounter can persist and become more powerful and dangerous. There's not a lot of "treasure" here, other than the magical materials the delvers went to collect. If the monsters use weapons, they are often elements of the environment -- broken off stalagmites with a convenient grip and edge like a falchion, say.