- keep, donjon, dungeon - the main tower within the walls of a medieval castle or fortress
--1 is a kind of stronghold, fastness
--1 is a part of castle
--1 has particulars: Black Hole of Calcutta - dungeon - a dark cell (usually underground) where prisoners can be confined
--2 is a kind of cell, jail cell, prison cell
--2 has particulars: oubliette