Mammoth Cave National Park

Location: Kentucky, USA

Size: 52,830 acres

Under a swath of Kentucky hills and hollows is a limestone labyrinth that became the heartland of a national park. The surface of Mammoth Cave National Park encompasses about 80 square miles. No one knows how big the underside is. More than 365 miles of the five-level cave system have been mapped, and new caves are continually being discovered. Two layers of stone underlie Mammoth's hilly woodlands.

A sandstone and shale cap, as thick as 50 feet in places, acts as an umbrella over limestone ridges. 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, a United Nations World Heritage site and the core area of an international biosphere reserve, still is as "grand, gloomy, and peculiar" as it was when Stephen Bishop, a young slave and early guide, described it. By a flickering lard-oil lamp he found and mapped some of Mammoth's passages. Bishop died in 1857. His grave, like his life, is part of Mammoth; it lies in the Old Guide's Cemetery near the entrance.

Most visitors see the eerie beauty of the caverns on some of the 10 miles of passages available for tours. Rangers dispense geological lore and tell tales about real and imagined happenings 200 or 300 feet down. The tours are hikes inside the Earth; uphill stretches can be hard going for some visitors. Few seem frightened; people terrified by darkness or tight spots naturally avoid caves. Rangers say they rarely have problems guiding the 390,000 men, women, and children who venture below yearly.

Mammoth does not glamorize the underworld with garish lighting. You never forget that you are deep in the Earth. And nowhere else can you get a better lesson in the totality of darkness and the miracle of light. Usually on a tour a ranger gathers everyone and, after a warning, switches off the lights. The darkness is sudden, absolute. Then the ranger lights a match and the tiny dot of light magically spreads, illuminating a circle of astonished faces.