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Mammoth Cave National Park
Kentucky park above the longest known cave system on Earth
Beneath the wooded hills of south-central Kentucky runs a labyrinth so vast that explorers are still adding to it. Surveyors have mapped more than 426 miles (686 km) of passages in the Mammoth Cave system, making it the longest known cave system in the world by a wide margin. The caves formed as rainwater and the Green River slowly dissolved thick limestone beds capped by a sturdy layer of sandstone, which kept the upper passages from collapsing. The result is a stacked maze of dry canyons, vertical shafts and vast rooms, with the river still carving the lowest levels today.
People have entered these passages for thousands of years. Native Americans mined minerals deep inside, and during the War of 1812 enslaved laborers extracted saltpeter for gunpowder. In the 1830s and 1840s Stephen Bishop, an enslaved guide, explored and mapped miles of new passages and became the cave's most celebrated early explorer. Congress authorized the park in 1926, but land acquisition through often bitter eminent domain proceedings delayed its establishment until July 1, 1941. Mammoth Cave became a World Heritage Site in 1981 and an International Biosphere Reserve in 1990.
The park covers about 84 square miles (219 km²) of forest above ground, threaded by the Green and Nolin rivers. Ranger-led tours range from short walks to strenuous crawls, and the surface holds trails, campgrounds and river routes for canoes. Blind cave fish, eyeless crayfish and other species adapted to total darkness live in the underground waterways, and the park was named an International Dark Sky Park in 2021.