Argument of the Gods
Dungeons don't just happen by accident. OK, some dungeons happen by accident. But some dungeons were brought about by something. Like when the gods start talking. Gods can't just talk, you see. Their words make things happen. When the gods really get arguing, all kinds of things come into the world, like the platypus (or the dreaded razor tooth giant platypus), the Leaning Tower of Pisa, or a plurality of bald Kings of France. Sometimes what comes into being is a dungeon.