The World’s Longest Known Cave System Hides Waterfalls, Crystal Flowers, and Blind Fish Deep Beneath Kentucky

The Mammoth Cave, Kentucky

Four hundred miles of pure darkness, five levels of twisted passages, and one cave system to rule them all. This is Mammoth Cave, Kentucky’s underground behemoth complete with a River Styx.

Most of Mammoth Cave is Unexplored

The cave system has been evolving over millions of years, with significant geological formations dating back to the Mississippian period (approximately 359 to 323 million years ago).

The cave measured 420 miles in 2021 but has surpassed 426 miles of surveyed passages as of 2022. The cave network has five different levels that go as deep as 379 feet below ground (check keyhole passages like Fat Man’s Misery).

Research teams used modern laser scanning tools along with traditional measuring equipment, discovering more than 400 unique rock formations along the way.

The Kentucky Cave Fish

Both north and south species of this fish lives in the dark waters of Echo River, where it has changed over time to survive without ever seeing light. These fish look almost see-through and have no eyes, but they can feel their way around using more than 35,000 special sensors.

These unusual fish can go up to a year without eating, using less energy compared to flappy cousins in the streams. The cave’s underwater world is also home to two types of blind crayfish and dozens of cave crickets, while endangered Indiana bats roost in its upper chambers.

The Cave Self-Regulates Its Temperature

When the air pressure changes outside Mammoth Cave, the entire cave system transforms into a giant lung (metaphorically). The cave moves more than 200 cubic feet of air every minute through its passages through convection.

When the outside air pressure drops slightly, the cave releases air so fast it can create winds up to 35 miles per hour. This natural air circulates the atmosphere like a thermostat, keeping the cave at around 54 degrees Fahrenheit all year round, no matter what the weather is like outside.

Crystal Flowers Grow on Mammoth Caves Walls

Inside a part of Mammoth Cave called Cleaveland Avenue, you can see delicate crystal formations that look just like flowers growing from the rock.

These gypsum crystals can grow up to 8 inches long, with petals that curl in beautiful patterns. The crystal flowers form very slowly when water containing dissolved minerals seeps through the limestone walls.

Some of these formations in Crystal Avenue have been growing for more than 20,000 years. Try the Snowball Room, at the end of Cleaveland Avenue. Gypsum flowers cover the ceiling in large clumps.

Preserved Bodies Have Been Found Here

Native Americans first explored these caverns 5,000 years ago for minerals like gypsum and mirabilite. Researchers found several naturally preserved bodies in the cave’s upper rooms in 1935.

The steady temperature and moisture kept the remains of a Native American woman in Short Cave from the early 1800s in remarkably good condition for thousands of years. Along with the bodies, researchers have found moccasins and cane torches, including tools for mining that show how these ancient people lived.

There’s a Canyon That Stretches for Literal Miles

Mammoth Cave’s Grand Avenue runs for 4 miles and takes about 4 to 5 hours to complete. Ancient underground rivers carved this huge passage through limestone rock, creating chambers exceeding 100 feet in height. The canyon began forming more than 10 million years ago when rainwater turned acidic and slowly dissolved the limestone.

Sections of the Cave Have Their Own Climate

The cave’s vast network of passages creates small climate zones. The Frozen Niagara section of the cave faces water seepage and preserves frozen waterfalls and intricate mineral deposits.

These varying conditions have created special environments for 1,300 plant species and 39 endangered cave-dwelling species. The Speroid Passage remains humid, giving life to fungi and microbes, while amphipods, a type of shrimp-like crustacean, dwell deep in the cave waters.

Even the central passages host gray and little brown bats, while the Indiana sleeps along the entrance in winter.

It Once Supplied Gunpowder for the War of 1812

During the War of 1812, workers dug up 400,000 pounds of saltpeter (Calcium nitrate, derived from bat guano deposits) from Mammoth Cave’s soil to make gunpowder for the military.

Enslaved workers moved tons of dirt through a system of wooden pipes and filtering boxes. The cave’s dry air has preserved many of these wooden containers, along with old tracks for carts and marks left by tools.

You can still see the original wooden pipes (over 200 years old ) that were held together with square nails back in the day.

Two Rivers Flow Underground

Deep in Mammoth Cave, the Echo and Styx River, continue to shape new passages. The Echo River is several miles long and serves as the main underground stream of Mammoth Cave.

The River Styx is known for its reverse flow patterns. Scientists have found that rain enters the cave through sinkholes and travels through these rivers before flowing out into the Green River above ground.

They added harmless fluorescent dye to the water, which can take anywhere from 4 hours to 3 days to travel through the cave system.

It Was a Once a Tuberculosis Hospital

In 1842, a doctor named John Croghan built a hospital inside Mammoth Cave’s main chamber to treat people with tuberculosis. He set up two stone cabins and eight tuberculosis huts that you can see along Broadway within Mammoth Cave Historic District today.

The hospital ran for five months and treated 11 patients while five are known to have died according to sources. Though the treatment didn’t work, you can still see the remains of these buildings 300 feet underground, including their stone bases and air vents.

Cave Dwellers Adapt to Darkness

The Mammoth Cave Spider shows how cave animals can change to survive in complete darkness.

These spiders rely on specialized hairs and sensors on their legs to detect vibrations and movements in the dark, 3 feet away without any light. They have lost all color and can live without eating for up to eight months.

You might also come across cave-dwelling beetles, such as Neaphaenops tellkampfii feeding on the eggs of cave crickets.

Longest Cave Tour in North America

The Wild Cave Tour takes experienced cavers on a six-hour journey through 5.7 miles of Mammoth Cave’s most challenging passages.

People on the tour crawl through spaces only 9 inches wide and climb over ancient rock formations. The path goes 300 feet underground and shows visitors parts of the cave that few people ever see.

Only 14 people are permitted on each tour, and it is only done on the weekends starting at 9 a.m.​