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A tour of America's national parks

By: Catie Leary on Dec. 18, 2009, 10:53 a.m.
Formations in Mammoth Cave National Park

Photo: blmurch/Flickr

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Mammoth Cave National Park

Mammoth Cave in Kentucky is the longest cave system in the world, but it's the variety of spaces that you're likely to remember — from claustrophobia-inducing nooks to spaces rivaling Grand Central Station. It's a great family stop, too, because there are hikes below and above ground for all skill levels.