Fodor's Expert Review Speedwell Cavern
This is the area's most exciting cavern by far, with 105 slippery steps leading down to old lead-mine tunnels blasted out by 19th-century miners. Here you transfer to a small boat for the claustrophobic ¼-mile trip through an illuminated access tunnel to the cavern itself. At this point you're 600 feet underground, with views farther down to the so-called Bottomless Pit, a cavern entirely filled with water. An on-site shop sells items made of Blue John, a mineral found nowhere else in the world.