6. Gorgeous Mammoth Caves in United States
Mammoth caves are one of the most beautiful ones across the world. They are found in U.S. National Park in Central Kentucky. They feature 365 miles of subterranean passageways making them the longest cave systems in the world.
They consist of a giant sinkhole known as Cedar; the most attracting feature in these wonderful places. The cave system was converted to a national park in 1941.