Peak Cavern, also known as the Devil's Arse, is a popular show cave in Castleton, Derbyshire, England. It boasts the largest cave entrance in Britain and is almost entirely natural, with only a small artificial section added for accessibility. The cave was once home to troglodytes who lived inside and made a living from rope making. You can explore passages like "Lumbago Walk" and caverns like "The Great Cave" and "Roger Rain's House." The cave has also hosted concerts and events, adding to its unique charm and appeal.