World’s Largest Cave, Son Doong, Malaysia

The cave was found in 1991 by local man Ho Khanh. In 2009, a group of British cavers led by Howard Limbert explored the cave’s interior, only then realizing that it was possibly the greatest cave in the world. Son Doong Cave has dethroned Malaysia’s Deer Cave as the world’s largest.

The water and limestone that carved it over millions of slow, patient years have created spectacular and unique formations. Occasional collapses in the roof have allowed underground jungle ecosystems to form, and with them, all-new species that have never been seen anywhere else. Rare cave pearls, ancient fossils, and towering stalactites form around a river running through the caves, which are so large that they form their own clouds.

Now that the caves have been thoroughly explored, the government has granted tour operators permission to host treks through the caves, which have already begun operating this summer