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This week on our national parks journey, we head to the southeastern state of Kentucky. Here you will find rolling hills and thick green forests.

But beneath the land is a strange and silent underground world. One early explorer described it as “grand,” “gloomy” and “peculiar.”

Welcome to Mammoth Cave National Park!

Mammoth Cave is the longest known cave system in the world. It is two times as large as the world’s second-biggest cave system. Its size helped give it its name. Mammoth as an adjective means “extremely large.”

Mammoth Cave National Park is in Kentucky’s Green River valley. The park covers over 20,000 hectares. It protects the river valley and hilly land, as well as the vast underground cave system.

'Thanksgiving Hall' section of Mammoth Cave
'Thanksgiving Hall' section of Mammoth Cave

The U.S. Congress formed Mammoth Cave National Park in 1941. Forty years later, it was named a World Heritage Site. And in 1990, it became a UNESCO Biosphere Reserve site.

Researchers and explorers have mapped than 600 kilometers of passageways in Mammoth Cave. And scientists continue to explore it.

Water formed the cave over millions of years. Other than the Green River, few sources of water exist above ground. That is because water seeps quickly into the earth. Soil made of broken-down limestone absorbs the water. It has created a vast and complex system of chambers and passageways.

A delicate and unique ecosystem exists inside the cave. More than 100 kinds of animals live in Mammoth Cave. Some of them live their whole lives in total darkness. Cave shrimp and many other kinds of eyeless, colorless species can be found.

Cave crayfish at Mammoth Cave National Park
Cave crayfish at Mammoth Cave National Park

Mammoth Cave was once home to about 10 million bats. They included species like Indiana bats, big brown bats, little brown bats and the eastern small-footed bat. Now, they number in the thousands.

Humans first entered Mammoth Cave about 4,000 years ago. They discovered uses for minerals inside the cave. Researchers describe them as “primitive miners.” Humans explored Mammoth Cave for nearly 2,000 years. Then, their exploration appears to have ended.

The caves would not be explored again until the end of the 1700s.

Many stories name John Houchins for re-discovering the cave. They say he was hunting in the area when he came upon a black bear. The bear was close to the entrance of the cave. Houchins shot the bear, but he failed to kill it. The bear ran, and Houchins followed. It led him into the cave. Experts do not agree on the exact year of Houchins’ discovery, and some people question the story entirely.

The historic entrance of Mammoth Cave
The historic entrance of Mammoth Cave

Slaves played many important roles at Mammoth Cave during the 1800s. During the War of 1812, slaves mined the cave for a mineral called saltpeter. It was used to produce ammunition used during battle.

And in 1816, slaves began guiding visitors on cave tours. At the time, the cave was still privately owned.

One of the greatest early explorers of the cave was a slave named Stephen Bishop. He arrived at Mammoth Cave in 1838, when he was a teenager. He learned the tour paths from white guides.

Stephen Bishop
Stephen Bishop

But Bishop wanted to push beyond the cave’s toured areas. He set off to explore parts of the caves no human had ever seen. Bishop and a companion sought to cross an area called the Bottomless Pit. Its unknown darkness had stopped people from trying to go beyond it.

But fear and darkness did not stop Bishop. The areas he discovered beyond Bottomless Pit are still open to visitors today. Bishop started naming different areas of the cave he discovered -- Fat Man’s Misery, Cleaveland Avenue, and Mammoth Dome, among others. He was also the first to discover a river running through the cave.

Mammoth Dome, named by Stephen Bishop
Mammoth Dome, named by Stephen Bishop

Bishop created a map of Mammoth Cave in the early 1840s. It included 16 kilometers of passageways. Most of the passages had been discovered or explored by Bishop himself. His map remained in use for more than 40 years.

Bishop gained his freedom in 1856, but he died the next year at the age of 37. His grave lies within Mammoth Cave National Park.

It was Bishop who described Mammoth Cave as “grand, gloomy and peculiar.”

For national park visitors who venture into the cave today, Bishop’s description remains true. About 500,000 people tour the cave each year. They are among the more than two million visitors to the park itself.

Mammoth National Park offers campsites for those who want to sleep under the stars. There is also a hotel in the park. And there are plenty of activities outside of the cave. People ride horses on the more than 100 kilometers of park trails. They also fish and boat in the park’s rivers.

A person kayaks on the Green River
A person kayaks on the Green River

But the main draw of Mammoth Cave National Park remains the dark mystery of an underground world, with so much more to discover.

I'm Caty Weaver.

And I’m Ashley Thompson.

Ashley Thompson wrote this story with materials from the National Park Service. Caty Weaver was the editor.

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Words in This Story

gloomy - adj. somewhat dark

peculiar - adj. not usual or normal

mammoth - adj. very large

vast - adj. very great in size, amount, or extent

seep - v. to flow or pass slowly through small openings in something

primitive - adj. of, belonging to, or seeming to come from an early time in the very ancient past

venture - v. to go somewhere that is unknown, dangerous, etc.

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This year, the U.S. National Park Service turns 100. America’s 28th President, Woodrow Wilson, formed the National Park Service in 1916 to “protect the wild and wonderful landscapes” in the United States.

Today, the National Park Service protects over 400 parks and historical sites from coast to coast. Every week, VOA Learning English will profile one of the sites within the National Park Service.

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