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9 jaw-dropping caves

Mammoth Cave

Photo: Dave Bunnell

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Mammoth Cave

As the longest known cave system in the world, it’s no wonder Mammoth Cave was established as a national park. The Kentucky cave has 367 miles of passageways, and it’s widely believed that many more miles have yet to be discovered. The cave's name originates from it's vast length, as opposed to the popular (yet false) belief that it has something to do with the now-extinct woolly mammoth.