Treak Cliff Cavern is a genuine wonder in the heart of the Peak District. Treak Cliff Hill is the only place in the world where Blue John Stone, a rare form of fluorite with beautiful colours occurs naturally. The self-guided audio tour explains how Blue John Stone was formed, how miners in the 1700s constructed a tunnel using only hand tools to reach the Blue John Stone deposits within the hill, and you can see incredible veins of the stone across the cavern roof and walls.