The world’s longest cave system and a UNESCO World Heritage Site. Mammoth Cave was established as a national park on July 1, 1941 although people have been touring the caves since the 1800’s. Currently, over 400 miles of the cave system have been explored and mapped, with new discoveries being made all of the time. Bats dwell inside of the cave. Karst cave system. The cave was formed in a layer of limestone under the Flint Range in the western foothills of the Appalachians. The length of the explored part of the cave system is 676 km. In the surveyed part there are 225 underground passages, about 20 large halls and more than 20 deep shafts. Depth – 115 m. The cave was discovered by American pioneers in 1797.