About 40 kilometers south of Salzburg, Austria, in the market town of Werfen, lies the largest ice cave in the world. It's called Eisriesenwelt, which means "World of the Ice Giants" in German. It was first explored in 1879 by scientist Anton Posselt. Long before he arrived, locals knew about the cave and believing it was the entrance to hell — and they avoided it. The cave extends 42 kilometers, though only the first kilometer or so is covered in ice, which was formed when snow from outside the cave melted, drained in the cave and froze again during winter. Today the Eisriesenwelt is a popular tourist destination, with about 200,000 visitors every year.