The longest cave system in the world is the Mammoth–Flint Ridge cave system in central Kentucky, also known as Mammoth Cave.
The Mammoth–Flint Ridge cave system is more than 350 miles (563 km) long.
Explorers are still discovering new passages in Mammoth Cave.
The cave was formed over the past 10 million years by slightly acidic rainwater filtering through the cracks of a limestone ridge, creating underground rivers that gradually carved out the cave.
It features many interesting rock formations and several lakes, rivers, and waterfalls.
Several types of blind animals live in the cave, including fish, beetles, and crayfish.
Visitors can tour the cave at Mammoth Cave National Park.