More than 20,000 caves dot the United States, according to the National Speleological Society, which also offers up these underground superlatives:
- Total number of miles mapped: Nearly 5,000
- Longest Cave: Mammoth Cave, Mammoth Cave, Ky., 390 miles
- Deepest Limestone Cave: Lechuguilla Cave, Eddy County, N.M., 1,604 feet
- Largest underground chamber: Carlsbad Caverns’ Big Room, Carlsbad Caverns, N.M., 33,210 square meters
- Longest sea cave: Painted Cave, Santa Cruz Island, Calif., 1,227 feet
- Longest underwater cave: Wakulla-Leon Sinks Cave System, Leon and Wakulla counties, Fla., 32 miles
- Longest Gypsum Cave: D.C. Jester Cave System, Greer County, Okla., 6 miles