In 1885, rancher and miner Absalom Lehman discovered this underground wonder—a single limestone and marble cavern 2½ miles long. Inside, stalactites, stalagmites, helictites, flowstone, popcorn, and other bizarre mineral formations cover almost every surface. Lehman Caves is one of the best places to see rare shield formations, created when calcite-rich water is forced from tiny cracks in a cave wall, ceiling, or floor. Year-round the cave maintains a constant, damp temperature of 50°F, so wear a light jacket and nonskid shoes when you take the tour, which takes you ¼ mile into the cave. Go for the full 90-minute tour if you have time; during summer, it's offered four or five times per day, as is the 60-minute tour. Expect daily tours during the winter. Children under age five are not allowed on the 90-minute tours, except during the winter; those under 16 must be accompanied by an adult. Take the 0.3-mile Mountain View Nature Trail beforehand to see the original cave entrance and Rhodes Cabin, where black-and-white photographs of the park's earlier days line the walls. If you're planning a visit during a holiday, get your cave tickets in advance as the tours can book up quickly.