Miror B.'s Hideout is actually made up of two distinct parts. The first section is a rotting, run-down warehouse to the northeast of Pyrite Town. Inside the warehouse, there's also an elevator that will take riders down into The Under. It's a fairly easy place to navigate around, but the large amount of guards makes progression difficult.
The top of the warehouse connects to the entrance of Pyrite Cave, an abandoned coal mine where most of Miror B.'s force hides. The very depths of the cave are actually a jumble of broken sewer pipes and underground lakes.
Miror B. himself stayed in one of the drier areas.
Most of the peons in Miror B.'s Hideout use Lotad and its evolutions, no doubt to mimic Miror B. himself, whose favorite Pokémon is Ludicolo.
