Fortress Island was a small island located on Earth in the English Channel. was incarcerated in the prison on Fortress Island "forever", and was later visited by the Third Doctor. The Master escaped soon afterwards with the assistance of George Trenchard. (TV: The Sea Devils) After it ceased to be a prison, it became a retirement home for the compromised ex-UNIT operatives, who would pose a security risk. (AUDIO: The Screaming Skull)