For decades, geologists have known that Vietnam is home to some of the world's most spectacular caves, many of them largely unexplored. Now husband-and-wife cavers have documented perhaps the world's largest: Hang Son Doong, big enough in places to accommodate a New York City block of skyscrapers.
The cave in the Annamite Mountains contains a river and jungle (its name translates to "mountain river cave") and even its own thin clouds, and its end remains out of sight. It's part of a network of about 150 caves in central Vietnam near the Laotian border.
Many more photographs taken in Hang San Doong and other newly explored caves have been published in theJanuary issue of National Geographic and on its website, where you can view larger images. The site also has an interactive graphic of the river cave's path.
By Brett Michael Dykes