Mammoth Cave National Park is a 1 1/2-hour drive from Louisville, Kentucky, or longer if you take the tree-lined scenic route past Lincoln's birthplace of Hodgenville-and about the same from Nashville.
The Introduction to Caving tour usually sells out, so it's a good idea to make reservations ahead of time. Park information and tour reservations are at nps.gov/maca The park doesn't charge entry fees, but cave tours cost from $4 to $46. The cave is about 54 degrees year round, but you'll stay warm enough on the Intro to Caving tour without a jacket. The park doesn't allow backpacks or fanny packs in the cave; check other restrictions online. Accommodations are available in the characterless but convenient Mammoth Cave Hotel, right in the park, or in nearby Cave City. And, of course, this is a national park, so you can rough it in the campground if you prefer.