The umbrella leaks at places called sinkholes, from which surface water makes its way underground, eroding the limestone into a honeycomb of caverns. Mammoth, the world's longest known cave system ...

While you wouldn't guess it from above ground, the park features 365 ... inside dance on the cave walls. While the caves are definitely the most unique element of Mammoth Cave National Park ...

Cave explorer Floyd Collins got trapped in Sand Cave in Kentucky 100 years ago and later died. The incident drew national attention and helped lead to the creation of Mammoth Cave National Park.