December 17, 2010
Hang Son Doong Photo
Photograph by Carsten Peter, National Geographic
This Month in Photo of the Day: Travel and Adventure Photos
A half-mile block of 40-story buildings could fit inside this lit stretch of Hang Son Doong, which may be the world's biggest subterranean passage.
See more photos of the January 2011 story "Conquering an Infinite Cave."
See photos of Vietnam »
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