Son Doong, the world's largest cave passage — big enough to fit a skyscraper — is deep inside a Vietnamese jungle. Exploring the dark caverns, home to beautiful rock formations and a river, takes days.
Imagine, in the 21st century, discovering a marvel on par with Mount Everest or the Grand Canyon. It happened, in 2009, with the revelation of the largest cave passage in the world. It's in Vietnam a… [+9457 chars]
