-Carlsbad Caverns National Park, Carlsbad, NM. An 8.2-acre Big Room (partially wheelchair-accessible); ranger- and self-guided tours. Mexican free-tail bats exodus, summer twilights.
-Howe Caverns, Howe's Cave, NY. An elevator takes you 156 feet below the surface; some tours include boat rides.
-Mammoth Cave National Park, Mammoth Cave, KY. More than 390 miles of explored caves. Variety of guided tours.