Mam Tor is a hill situated near Castleton on the southern side of the Dark Peak of Derbyshire, England. It is formed of rocks of carboniferous age and the base is composed of black shales. At the bottom and close to it are four caves, including Speedwell Cavern, Peak Cavern, Treak Cliff and Blu John Cavern. In a clear day offers amazing views of the Manchester City Centre, Stockport and Winter Hill. The most remarkable characteristic is the active landslip, invading the southeast side almost to the summit, and discontinuing the ramparts of the hillfort, unless its builders used it as part of the defences.