Mr Weasley says that the Department of Mysteries is a top-secret organisation, and that he has no idea what the Unspeakables, the wizards who work there, get up to.
The main hall of the Department of Mysteries is a large, circular room. Everything in the room is black, including the floor and ceiling, with identical, unmarked, handleless black doors set at intervals along the walls. The circular wall of the room begins to rotate very quickly after the group have entered. It stops almost as soon as it has started, designed to prevent visitors from knowing which door they came in through.
Each door off the main hall leads to a different chamber, including the Brain Room, the Death Chamber and the Time Room.
