Castleton sits at the head of the Hope Valley with four separate showcaves within walking distance. Peak Cavern (the largest cave entrance in Britain, known locally as the Devil's Arse), Speedwell Cavern (boat trip underground), and Blue John Cavern and Treak Cliff Cavern, both sources of Blue John, a semi-precious fluorite mineral found nowhere else on earth.
Mam Tor ridge above the village is an easy 40-minute climb to one of the best ridge walks in the Dark Peak. Do the ridge first, then a cave tour, the combination is the best single day in the northern Peak District.