Mammoth Cave National Park

If you love caves, you'll love Mammoth. It boasts the longest cave system in the world with more than 365 miles under the Kentucky hills. Aspiring spelunkers can take a three-hour Introduction to Caving trip with their parents or opt for a parent-free Trog Tour. Participants don a hard hat and headlamp on both tours. Other guided tours include the Snowball Tour (featuring an underground concession stand) and the lantern-lit Violet City and Great Onyx tours.