Dungeon.

A dungeon is a type of prison, usually an underground room or cell, in which prisoners are held. Dungeons are generally associated with medieval castles, though their association with torture probably derives more from the Renaissance period. They are closely connected in concept both to the prison and the oubliette, and the words are sometimes used interchangeably. In the popular imagination, a dungeon is claustrophobic, strong, damp, and located in a castle under the direct control of a medieval lord. This intentional unpleasantness and personal control over a dungeon contrasts to the modern prison, which provides a civil function.