Mammoth Cave National Park, Kentucky
Drive time: 6 hours

With over 400 mapped miles, Mammoth Cave National Park, just outside Bowling Green, Kentucky, is the longest known cave system in the world. The only way to see its many subterranean rooms and passageways is to join a tour. There are more than 15 options, including accessible routes with an elevator to carry you 26 stories down, but for those who don’t fear a little adventure (and more than a little claustrophobia), the six-hour Wild Cave Tour ($79) is the way to go. The guided five-mile trek will have you scrambling over rocks, crawling through tight spaces, and climbing cave walls. Reservations are recommended, and participants must be 16 or older. 

While there More than just caves, the UNESCO-designated national park spans nearly 53,000 acres of rolling hills and forested trails. Take the half-mile Echo River Spring Walk, a ranger-led hike, to learn more about Mammoth’s karst landscape.