Mammoth Cave Is the Longest Known Cave System in the World

The longest cave system anyone has found is under the hills of Kentucky. The US National Park Service describes Mammoth Cave National Park as a place of rolling hills, deep river valleys, and the world’s longest known cave system. One word in that description deserves attention, and it is known. A cave system can only be measured as far as people have explored it, so the title belongs to the longest system discovered so far and leaves room for more to be found. The park is valued for more than its length. According to the park service, it is home to thousands of years of human history and a rich diversity of plant and animal life, and it has been recognised as a UNESCO World Heritage Site.