The Bass Rock, or simply the Bass, is an island in the outer part of the Firth of Forth in the east of Scotland. Approximately 2 km offshore, and 5 km north-east of North Berwick, it is a steep-sided volcanic plug, 107 m at its highest point, and is home to a large colony of gannets. The rock is uninhabited, but historically has been settled by an early Christian hermit, and later was the site of an important castle, which after the Commonwealth period was used as a prison.