A hidden universe beneath Kentucky: How Mammoth Cave stretched 686 kilometres underground | World News
PC: National Park Service The Mammoth Cave, located deep under the hills of Kentucky, is the longest cave system in the world with an officially surveyed length of 426 miles (686 kilometres) according to the U.S. National Park Service. Each year, through ongoing mapping expeditions, new miles are added to this ‘endless’ cave system, which…