The Blue John Cavern lies just outside Castleton inside Treak Cliff. It's still a functioning mine, but the miners also take regular tours down into the caverns to show visitors around this phenomenal place.
Blue John? But the stone is purple... At the lighter end, however, it's a range of blues and yellows, and it's possible that the name came from when the stone was worked in France, and known as the 'bleu jeune' stone. There are other theories though, and part of the attraction of the stone is perhaps its mystery as well as its rarity. The stone is a 'fluospar', and the coloured banding is unmatched elsewhere in the world. Eight of fourteen known veins are accessed through this one mine.
Caves are often associated with stalactites and stalagmites, great glorious mineral deposits. The way these caves have formed, however, means that no stalactite is over about a foot in length. Instead you see amazing 'waterfalls' running down the caves sides, unlike anything I've seen.
Stories about the mine abound, and extremely friendly guides are more than happy to share them. Now, for example, electric lights line the route. In one high cavern there are signs of the two former methods of lighting the area. Visitors could choose from a candlearbre hoisted to the ceiling, or short flashes of ignited magnesium. There is a certain beauty to imagining our forebears exploring the caves before us, too.
You should be careful as you descend. These rocky waterfalls are a sign of the real water still seeping through the rock. On a bad day we were told an umbrella was warranted. Even on a good day, the rocks can be slippery and you need to hang on to the handrails. The trip is advertised as inappropriate for people who are unstable or suffering from bronchitis, and for babes in arms.
The caves are natural, formed by melt water rivers from the ice age, with only the staircase being manmade. At some points you have to duck as the low ceilings close in around you, but most of the time there is plenty of space. They say that the lower you go, the bigger the caves become, so that instead of feeling claustrophobic you instead experience great vaulted areas.
In one section, a recess of Blue John has been left for visitors. The stone is extremely fragile, and needs to be mined carefully, reinforced with resin in order to be workable. Each seam is only a few inches deep, so you're never going to get huge items out of it. Things made from it are an auction-hunter's dream: beautiful, individual, and unexpectedly valuable given the rarity of the stone.
At the end of the tour you come to a point where the caverns extend further, but not for tourists. Footprints in the clay betray where intrepid explorers have gone further. Apparently a local man has made over 100 trips to the end of the caverns, hunting out blocks of stone submerged in the clay.
The tour lasts over an hour, by the time you've descended, looked around and climbed back up again, so although it's not cheap, it is very much worth it. The shop sells small items made from Blue John. More interesting ranges of jewellery can be found down in Castleton, but they also sell small unworked pieces very cheaply, which make good small souvenirs, or a project for someone to try their hand at working. A counter sells hot drinks and snacks, which might be a good idea after a walk in the cold caverns, in a windswept area.