Biggest Cave in the World Discovered

This is the world’s largest mammoth cave (262-by-262 feet (80-by-80 meters) in most places), one of 20 discovered last year in Vietnam. It is so big, the bottom is out of sight! Not only there are jungles inside it. The roof of the cave fell in and let sunlight in and all kinds of vegetation soon followed, and we're not just talking some shrubs. It seems that a whole jungle has sprouted up inside this cave!

The team found an underground river running through the first 1.6 miles (2.5 kilometers) of the limestone cavern, as well as giant stalagmites more than 230 feet (70 meters) high.

Some are amazed that in this day and age, caves so large can remain hidden, but researchers say that even though some locals may have known about the entrance, the sounds of the river were strong and intimidating, and no one dared explore it.

Some satellite images hint that caves even larger than this one await human exploration deep within the Amazon rain forest.