The word dungeon (or donjon) is Old French, sourced from the Latin "dominus", a lord. In its original medieval usage the donjon is the keep, the main tower of a castle which formed the final defensive position the garrison could retreat to when outer fortifications were overcome. It was the strongest, or only, tower in the Castle. There were no windows in the lower part of the tower in order to strengthen the walls. The donjon was a safe, if not uncomfortable, place to keep prisoners and was used mainly for this purpose, once more luxurious housing for the lord of the castle was constructured. An example is found at Bothwell Castle.

It has evolved to also mean an underground prison or vault, typically built underneath a castle. Although many real-life dungeons are simply a single plain room with a heavy door or with access only from a hatchway or trapdoor in the floor of the room above, the use of dungeons for torture, along with their association to common human fears of being trapped underground, have made dungeons a powerful metaphor in a variety of contexts.

In 1613 Anton Praetorius described the terrible situation of the prisoners in the dungeons in his book Gründlicher Bericht über Zauberey und Zauberer (Thorough Report about Witchcraft and Witches). He was one of the first to protest against all means of torture.

See also

• Oubliette