Jewel Cave ranks as the nation’s second largest cave with 151 miles explored as of June 2010. Just 13 miles from Custer State Park, itâ€Â™s worth the extra ride to see it, as well as Wind Cave National Monument, the nation’s fourth-longest cave. Both offer a variety of tours of escalating length and difficulty. Wind Cave’s most unique feature is itâ€Â™s delicate boxwork, but Jewel Cave will impress kids more with its glittering calcite crystals on the walls. Other features to intrigue budding scientists include moonmilk and hydromagnesite balloons. If you have squirmy toddlers in tow or infants in carriers, thereâ€Â™s an easy 20-minute Discovery Talk and chance to see one of the caverns. Older kids can handle longer cave explorations, which include a 105-minute lantern tour (ages 6 and up).