Deep beneath the rolling hills of south-central Kentucky lies a world that almost doesn’t seem real: miles and miles of twisting passages, giant domes, underground rivers, and creatures that have never seen the sun. Mammoth Cave has been drawing curious visitors for centuries, from ancient miners with cane torches to modern families with headlamps and plenty of questions. It’s a place full of legends, history, and jaw-dropping geology, and the more you learn about it, the more you’ll want to go underground yourself. Here are 25 fun facts about America’s most amazing cave.

1) Mammoth Cave is the longest known cave system in the world, with more than 420 miles of surveyed passages.

2) It’s roughly twice as long as the second-longest known cave on earth, and cavers are still mapping new passages every year.

3) The name “Mammoth” refers to the cave’s enormous size, not woolly mammoth fossils.

4) Mammoth Cave became a national park on July 1, 1941, making it the 26th national park in the country.

5) It’s a UNESCO World Heritage Site (1981) and an International Biosphere Reserve (1990), putting it in the same league as the Grand Canyon and Yellowstone.

6) The cave has been a tourist attraction since about 1816, making it one of North America’s oldest tourist destinations.

7) Native Americans explored the cave thousands of years ago, mining minerals like gypsum and leaving behind burned cane-reed torches, sandals, and gourds that are still being found today.

8) In 1935, guides discovered “Lost John,” the preserved body of an ancient miner who was crushed by a boulder around 2,000 years ago while digging for minerals.

9) According to legend, a hunter named John Houchin found the entrance around 1797 while chasing a wounded bear.

10) During the War of 1812, enslaved laborers mined saltpeter in the cave to make gunpowder, and the old wooden leaching vats and pipes are still in place.

11) Stephen Bishop, an enslaved guide who began leading tours in 1838, was one of the cave’s greatest explorers. He crossed the Bottomless Pit on a ladder and drew a famous map of the cave from memory.

12) In the early 1840s, a doctor built a tuberculosis hospital inside the cave, thinking the steady air would cure patients. It failed, but two of the old stone huts still stand underground.

13) The cave stays about 54°F all year long, so bring a light jacket even in July.

14) Mammoth Cave formed in thick layers of limestone capped by a tough sandstone roof, which is why many passages stay so large and dry.

15) The passages are stacked on five different levels, carved over millions of years as the Green River cut deeper into the land.

16) More than 130 species are regular inhabitants of the caves, including eyeless cavefish, cave crickets, and the endangered Kentucky cave shrimp, which lives nowhere else on earth.

17) Frozen Niagara is one of the park’s most famous formations, a massive flowstone that looks like a waterfall turned to stone.

18) The Star Chamber has a ceiling speckled with gypsum and dark manganese that, by lantern light, looks just like a night sky full of stars.

19) On the Historic Tour, visitors squeeze through Fat Man’s Misery, a narrow, twisting passage, and then stretch out in Great Relief Hall.

20) In 1972, explorers finally proved Mammoth Cave connects with the Flint Ridge cave system after caver Patricia Crowther squeezed through a crawlway nicknamed the “Tight Spot.”

21) During the Kentucky Cave Wars of the early 1900s, rival cave owners put up misleading signs and hired “cappers” to steer tourists away from their competitors.

22) In 1925, caver Floyd Collins became trapped in nearby Sand Cave, and the rescue attempt turned into one of the biggest news stories of the decade.

23) From 1886 to 1931, the little Mammoth Cave Railroad carried visitors to the cave, and its locomotive “Hercules” is still on display in the park.

24) The park’s longest walking tour takes about 4 hours and includes 1521 mandatory stairs with an optional 98 stairs in the drapery room.

25) Above ground, the park covers almost 53,000 acres of lush forest, rocky outcrops, rivers, streams, and over 80 miles of hiking trails, and it’s a certified Dark Sky Park, so the stars are just as impressive as the cave.

Mammoth Cave is the kind of place that sticks with you long after you climb back into the sunshine. Pick a tour, from easy wheelchair-accessible walks to the muddy, belly-crawling Wild Cave Tour, and book early, since summer tours sell out fast. Spend the rest of your trip canoeing the Green River, hiking the forest trails, and stargazing under dark Kentucky skies. Adventure doesn’t get much deeper than this.

Address: 1 Mammoth Cave Parkway, Mammoth Cave, KY 42259
Website: https://www.nps.gov/maca