A cave explorer stands before an imposing stalagmite–made of mineral deposits–near an entrance to the Xe Bang Fai River cave in central Laos.
An expedition in February 2008, co-led by veteran caver John Pollack, comprehensively mapped and photographed the 5.9-mile (9.5-kilometer) length of the little-known cavern for the first time.
The spelunking team encountered some of the largest rooms and most impressive structures of any river cave on Earth, Pollack said.
A river cave is any cave with an active water source flowing through it. – natgeo