dungeon dungeon /ˈdʌndʒən/

noun

1. () The main tower within the walls of a medieval castle or fortress  ( donjon , keep , dungeon )
   the main tower within the walls of a medieval castle or fortress
    The castle's dungeon was cold and damp, with thick stone walls.
   The castle's dungeon was cold and damp, with thick stone walls.
   
   
2. A dark cell (usually underground) where prisoners can be confined  ( dungeon )
   a dark cell (usually underground) where prisoners can be confined
    The castle had a dark, foreboding dungeon where prisoners were kept.
   The castle had a dark, foreboding dungeon where prisoners were kept.