The following is a list of the world’s 10 longest caves per length of documented passageways. Many passageways are still being discovered; this list is based on the latest verifiable data.
Caves are found around the world. The largest form in areas of karst landforms whose rocks erode easily and create caves. Preferable conditions for cave formation are adequate precipitation, enough plants and animals to produce ample carbon dioxide, and a landscape of gentle hills which drains slowly. The highest concentrations of long caves in the world are found in the Pennyrile of Southern Kentucky, United States, in the Black Hills of South Dakota, United States, and in the Yucatán Peninsula, Mexico.
1. Mammoth Cave 651.8 km (405.0 mi) near Brownsville, Kentucky, United States 1791 Mammoth Cave National Park, also a World Heritage Site
2. Sistema Sac Actun / Sistema Dos Ojos 346.7 km (215.4 mi) near Tulum, Quintana Roo, Mexico 1987
3. Jewel Cave* 292.7 km (181.9 mi) near Custer, South Dakota, United States 1900 Jewel Cave National Monument
4. Sistema Ox Bel Ha 270.2 km (167.9 mi) near Tulum, Quintana Roo, Mexico 1996 southern parts in Sian Ka’an Biosphere Reserve
5. Optymistychna Cave 236.0 km (146.6 mi) near Korolivka, Ukraine 1966
6. Wind Cave* 229.7 km (142.7 mi) near Hot Springs, South Dakota, United States 1881 Wind Cave National Park
7. Lechuguilla Cave* 222.6 km (138.3 mi) near Carlsbad, New Mexico, United States 1900 Carlsbad Caverns National Park
8. Clearwater Cave* 215.3 km (133.8 mi) Mulu National Park, Sarawak, Malaysia 1978 Gunung Mulu National Park, also a World Heritage Site
9. Fisher Ridge Cave System 201.6 km (125.3 mi) near Brownsville, Kentucky, United States 1981
10. Hölloch 200.4 km (124.5 mi) Muotathal, Switzerland 1875