Blue John Cavern

Blue John is a variety of fluorite banded in purple, blue and yellow, and the only workable veins in the world are in Treak Cliff at Castleton; the name is probably a corruption of the French bleu-jaune, though the derivation is not settled. Two caves are open on the hill, Blue John Cavern and Treak Cliff Cavern, both partly natural water-worn passage and partly miners' workings, and both still extract a few hundred kilograms a year under strict limits, worked into bowls and jewellery. The Blue John Cavern route drops through a series of large chambers including Lord Mulgrave's Dining Room, where a nineteenth-century mine owner is said to have entertained miners, and passes exposed veins in the walls. Roman finds suggest the stone was worked here two thousand years ago.

What you actually see

• The Blue John veins - banded purple fluorspar exposed in the passage walls.
• The water-worn chambers - natural cave enlarged by centuries of mining.
• The working extraction - a few hundred kilograms taken each year under limit.
• The finished stone - bowls and jewellery worked from the local mineral.

When to go

Year-round; the cave holds a steady temperature of around eight degrees, so a coat is needed in summer. Winter closures happen after heavy rain, when water levels rise in the lower passages.

Honest expectations

The tour is around two hundred and fifty steps down and back up, with low headroom in places, and is not suitable for anyone with mobility limits. Tours are guided at fixed times with no free wandering. The site sits on the closed section of the old A625 and is reached from the Winnats Pass side.

Nearby

Treak Cliff, Speedwell and Peak Cavern are all within walking distance; Castleton lies below.