According to the magazine, Son Doong cave is actually the longest natural cave system thus far known. Underground rivers eroding limestone deposits formed the cave approximately 2 to 5 million years ago.
It stretches about five kilometers in length, and opens out as high as 200 metres and as wide as 150 meters.
The cave starts to welcome international visitors in 2014.
The magazine also honoured Thailand’s Phraya Nakon and Morakot caves, New Zealand’s Waitomo Glowworm cave, Mexico’s Crystal Caves, Italy’s Blue Grotto, Scotland’s Fingal cave, France’s Lascaux, Russia’s Orda cave, Austria’s Eisriesenwelt, and China’s Reed Flute.