Cumberland Caverns, McMinnville

When surveyor Aaron Higgenbotham discovered Cumberland Caverns in 1810, he couldn't see its majestic pillars of dripping rock, its flowstone curtains, or its subterranean waterfalls. Stuck on a small ledge in the dark, Higgenbotham was as blind to the cave system's features—one of them a 2,000-foot-long cavern hall—as the eyeless crayfish that live there. His initial discovery nevertheless paved the way for nearly 200 years of speleological findings. Today, guides preserve this 32-mile National Landmark cavern by leading daily tours through its passages.

During tours, guides point out artifacts left by pre Civil War–era saltpeter mines, tunnels filled with rare gypsum deposits, and mysterious inscriptions reading "Shelah Waters - 1869" and "Millard Fillmore + Stacy." They lead guests among stalagmites and stalactites to a sound-and-light show that dramatically retells Bible stories, or into a domed hall that houses a hand-cut crystal chandelier rescued from a historic Brooklyn theater. It's in this last space that staffers organize banquets, weddings, and monthly live bluegrass concerts, or hold burial services for broken fax machines. They also lead visitors through the tight passageways of lesser-seen cavern segments during daytime or overnight spelunking trips.