Mammoth Cave National Park Travel Guide: Step underground into the world's longest known cave system—over 400 miles mapped and counting. Mammoth Cave is both mysterious and awe-inspiring, with labyrinthine passageways, towering chambers, and a history stretching back thousands of years. The cave system was formed over millions of years and has been used by humans for over 6,000 years. Above ground, rolling hills, rivers, and forests add to the adventure.