What Kentucky attraction is the world's longest cave?

Mammoth Cave is the world's longest known cave system, located beneath Mammoth Cave National Park in south-central Kentucky. Its surveyed passages stretch for more than 400 miles, although exploration continues and the measured total can change as new sections are mapped.

The cave formed in thick layers of Mississippian limestone. Rainwater absorbed carbon dioxide from the soil, becoming mildly acidic and gradually dissolving cracks and underground channels in the rock. Over immense spans of geological time, this process created the maze of chambers, shafts, and passageways known as Mammoth Cave.

People have used and explored the cave for thousands of years. Indigenous visitors entered it long before European settlement, and the cave became widely known in the 19th century for mining operations, tourism, and enslaved guides such as Stephen Bishop, who produced important maps and discoveries. Mammoth Cave National Park was established in 1941 and became a UNESCO World Heritage Site in 1981.

A common mix-up is confusing the world's longest cave with its deepest or largest single chamber. “Longest” refers to the total length of connected passages surveyed, not the depth of one vertical drop or the size of one room.