There are monsters that are unexplainable. One such kind of monster is the living dungeon. It is a living creature, or so they say. It worms its way through the ground, its many corridors stretched out like tentacles, until it finds the surface or some other underground place.
A living dungeon lures adventurers in with bits of treasure and knowledge. It knows what they want and dangles just enough to be an attractive nuisance. It kills off a few adventurers at a time, leaving some to escape to tell other—s about what they saw. It toys with adventurers, luring them deeper and then torturing them in horrible ways.
It can generate monsters, traps, and even reconfigure and reshape itself over time. The more it kills, the stronger it becomes, the more clever its magics.
Every living dungeon has a black heart, a secret place it guards carefully, for killing the heart kills the dungeon.