For all you prison enthusiasts out there, the oubliette is like the Cadillac of dungeons. An oubliette is a specific type of dungeon that has only one escape route — through a trap door in its ceiling.
An oubliette is very well constructed from the captor's point of view. With the only entrance and exit being in the ceiling far above where the prisoner stands, escape is pretty much impossible. You may have seen oubliettes depicted in horror movies — unsuspecting places where psycho killers keep their victims. As you may have guessed from the spelling, oubliette is a French word.