14. Mammoth Cave Park | Kentucky
Kentucky is home to the world’s longest known cave system, with over 400 miles explored. It welcomes fearless visitors to explore its dark and damp passages. Guided tours led by park rangers take you through dramatic passages adorned with geological formations, inspiring the inner explorer in you. These tours vary in length and include historical insights into the cave’s formation and its interactions with people and creatures. After several hours underground, appreciate the beauty of the clear waters and unspoiled nature through a bike ride or canoe adventure.