Carlsbad Caverns, New Mexico

Part of a major cave system, and now a National Park. Notable especially for its improvements, including a set of elevators that take you 750 feet below to the underground lunchroom. The bat amphitheater is another unusual feature of the park, where at certain times of the year, hundreds of thousands of bats rush out of the cave at once. The amphitheater is built directly under this aperture, so tourists can witness this phenomenon.