About midway between Louisville, Ky. and Nashville, Tenn. just off of I-65, Mammoth Cave offers a unique experience to millions of visitors each year: total darkness.
You've never really experienced darkness until you descend into the cave and a guide tells you the lights are about to be shut off. Don't worry -- someone knows how to turn them on again.
Your basic admission to Mammoth Cave comes at no charge, but the park offers some tours for the more adventuresome guests such as "Wild Cave" at a fee. On that tour, you'll don a miner's helmet and crawl through some tight spaces to see parts of Mammoth Cave most visitors never experience.
Since this is Kentucky, above ground there are equestrian trails you can explore.