Mammoth Cave, Kentucky
Photo Credit: Hulton Archive/Getty Images
Located in Kentucky, United States, the Mammoth Cave National Park is the most extensive cave system in the world. It is more than 400 miles long, doubling the length of Mexico’s Sac Actun, the world’s second longest cave system. On October 27, 1981, the park became a World National Heritage Site and an International Biosphere Reserve in 1990.
The cave system is regarded as very stable because the cave developed in thick Mississippian-aged limestone that is covered in a layer of sandstone. The National Park Service offers various cave tours that range from one to six hours in length for those who want to explore.
