Blue John Cavern

You descend into darkness, your guide's torch cutting through air that smells of stone and mineral deposits. Blue John Cavern, near Hope Valley, is one of Derbyshire's working show caves - still mined for the distinctive purple-blue fluorspar that Victorian Londoners couldn't get enough of. The mineral forms in veins through the limestone, catching light in ways that feel almost unreal down here.

The tour takes you through a series of chambers, some with names like the Waterfall Hall that hint at their drama. You'll see the actual mining operations - visitors aren't just gawping at pretty rocks, though there are plenty of those. The guides know their stuff and won't bore you with endless geology lectures. Allow about an hour underground, which is just right before claustrophobia kicks in or the kids start moaning.

It's genuinely worth the trip if you're based at Castleton Caravan and Motorhome Club Campsite or Laneside just down the road. The cavern works well for families who want something more active than a passive museum, though it's not a thrills-and-spills caving experience. Serious walkers often combine it with a ramble across the surrounding hills - the Hope Valley area is proper limestone country with decent footpaths.

Go mid-week if you can. Weekends pull crowds and the narrow passages get annoying. Wear decent shoes - it's wet and slippery in places, and a jumper even in summer.