Dungeon

The dungeons of Blarney Castle, Ireland.

A dungeon is a room or cell in a castle to keep prisoners. Most dungeons are underground, others are high up in towers.

An oubliette is a type of dungeon that can be entered by using a trapdoor in the ceiling. People were thrown into an oubliette from the ceiling and left there to starve or dehydrate to death, making it akin to immurement.