But there’s only one that’s home to the world’s longest cave. That 400-mile wonder can be found under the rolling Southern hills of Kentucky. So, explorers, pack those walking boots.

After the first day of trekking, the team set up camp in the vast opening of Hang En ... down through a hole in the cave roof, illumining the underground world. Filming this natural lightshow ...

Take an otherworldly journey through Hang Son Doong, the world's largest cave located in Vietnam. The cave is more than 500 feet tall, 650 feet wide, and 29,500 feet long. Video courtesy of Ryan ...

Why it's incredible: The cave is the biggest in the world and contains two jungles. Hang Son Doong is the world's largest known cave, with enough space in some of its passages to fly a Boeing 747 ...

Expedition leader Andy Eavis accesses a small algae-covered cave opening. He has been studying ... and for a decade afterward it stood as the world’s largest known cave passage.

Hang Son Doong is the world's largest known cave, with enough space in some of its passages to fly a Boeing 747 airplane through them. The limestone cavern sits beneath a lush jungle in Vietnam's ...

Hang Son Doong, the world's largest cave in Vietnam, was discovered in 1990 and is a breathtaking natural wonder. Formed over millions of years, this massive cave features towering stalagmites ...

This video shows a group of tourists taking a tour an ice cave underneath Vatnajokull glacier in Iceland. The glacier expands for 3,100 square miles and it is the largest in the country.

two of the top three largest known caves in the world. To get there, a punishing path and 90 percent humidity test even the fittest hiker. A walk for the fortunate few: Only a limited number of ...