The longest cave system in the world is named, rather fittingly, Mammoth Cave.
Found underneath Kentucky’s Mammoth Cave National Park, the cave has been mapped and explored at 686 kilometres (426 miles).
- It stretches 106 square metres and spans two countries – and it's home to over one hundred thousand scuttling residents
- It's 3 million years old, the size of Vikos Gorge and is home to one of the world's weirdest animals – the 'human fish'
For comparison, the coastline of the USA’s Washington state measures 400 kilometres (250 miles).
The cave is 118 metres (379 feet) deep, with five levels of passages. However, mappers believe there are many more miles left to be explored.
Humans have been using the cave for thousands of years, with First Nation peoples entering its shadowy depths around 5,000 years ago.
And in the 1840s, Stephen Bishop (an enslaved Mammoth Cave guide) made one of the first maps of the caves.
Before 1972, the nearby Flint Ridge cave system was considered to be the longest cave system in the world. However, cavers had suspected that the two were interconnected, due to signatures left by previous cavers in the walls.
So, on 9th September 1972, a group of explorers spent 12 hours in the Flint Ridge cave system in the hope of finding a connection between it and the Mammoth Cave system. They eventually found one, bringing the total length of the two connected cave systems to 232.39 kilometres (144.4 miles).
Since the connection was discovered in 1972, the whole system – known from then onwards as Mammoth Cave – has been further explored and mapped.
Mammoth Cave National Park was designated a UNESCO World Heritage site in 2002 due to its unique limestone cave formations and flora and fauna. It’s thought to contain the richest variety of cave-dwelling flora and fauna, with 130 species.
What animals live in Mammoth Cave?
Common cave crickets, fishing spiders, Allegheny woodrats and Rafinesque big-eared bats have all been found within the cave. The surprising cave beetle has also only been found in Mammoth Cave and the surrounding caves.
Southern and northern cave fish lurk in the cave’s waters and spend their entire life cycle there.
More species can also be found around Mammoth Cave National Park, including white-tailed deer, red-tailed hawks, bald eagles and eastern copperhead snakes.
A new species of ancient shark, named Macadens olsoni, was identified from a fossil in the park in 2025.
Top image: a photo of Mammoth Cave taken in 1999. Credit: scgerding/Getty Images
