1. a dark underground prison or cell, especially in a castle
Usage: historical
2. any dark, confined space resembling a prison

Examples

• The prisoners were locked in the castle’s dungeon.
• Medieval dungeons were cold and damp places.
• The basement felt like a dungeon with no windows.
• They explored the dungeon beneath the old fortress.
• The dungeon’s stone walls were covered in moss.
• He was thrown into the dungeon for treason.