It spreads over 9 kilometers in length and rises in places to 200 meters in height. Son Doong is the largest cave in the world. Located in central Vietnam (Southeast Asia), this limestone cave was formed around 2 to 5 million years ago. It is the result of successive erosions under the effect of the Rao Thuong River. Monkeys, bats and many species of birds inhabit the cave. Despite its millennial age, Son Doong was only discovered in 1991 by a local resident.