The first 1,000 feet might still have fallen rocks, even ice ... Wind Cave, nearly 4,000 feet in length, is closed in the protection of its important bat population. The caves, lava tubes, to ...

It’s very Icelandic: fire and ice, water and stone ... existing field of cooled lava. Over time, the ceilings of some of these tunnels partially collapse to form caves. There are some 500 ...