Mammoth Cave National Parknational park containing an extensive
system of limestone caverns in west-central Kentucky, U.S. It
was designated a World Heritage site in 1981. The park,
authorized in 1926 but fully established only on July 1, 1941,
occupies a surface area of 83 square miles (215 square km). In
1972 a passage was discovered linking the Mammoth Cave and the
Flint Ridge Cave System, which also is within the national park;
in 1983 a connection to Roppel Cave, which lies to the east of
the park, was found. The explored and mapped underground
passages of the entire multilevel system have a combined length
of more than 345 at least 400 miles (555 650 km), making it the
longest cave system in the world.  The caves were formed by the
dissolution of limestone by water, a continuing process; their
natural temperature is 54 °F (12 °C), with a relative humidity
of a high 87 percent. They contain underground lakes and rivers
and numerous unique geologic formations, including stalactites
and stalagmites, to whi