The Blue John Cavern is one of the four show caves in Castleton; Derbyshire; England. The cavern takes its name from the semi-precious mineral Blue John; which is still mined in small amounts outside
Treak Cliff Cavern is a show cave near Castleton in Derbyshire; England. It is part of the Castleton Site of Special Scientific Interest and one of only two sites where the ornamental mineral Blue John is excavated