The Xe Bang Fai River originates in the Annam Trung Sun Mountains on the border between Lao and Vietnam and flows across the Nakhai Plateau en route to the Mekong River. The Nakhai Plateau is composed of sandstones and massive carbonates layers which the river had dissolved to create Tham Khoun Xe, a subterranean channel 7 km long.
The cave is well-known to the Lao people who for centuries have fished in the river downstream from the cave exit, and scaled its entrance walls to harvest bird’s nests. The first European exploration were carried out in 1904, and then again in 1905 by French explorer Paul Macey and his team in bamboo rafts. No further attempts at exploration were made for the next ninety years after which, due to reasons unknown, the area was closed off to foreigners. The cave was finally opened with great reluctance in 2005-2006 for western kayakers. Since then, French and North American teams are operating in the area.
The entrance to the cave is a 60-meters tall arch at the base of an imposing limestone amphitheater over 150 meters tall. The river passage on average is 76 meters wide and 53 meters tall, but frequently exceeds 100 meters in width in places. The largest passage widths, the teams discovered, were 200 meters. The cave passage is between 4 to 12 meters deep. Many stalagmites here are more than 20 meters high, and some of the cave pearls seen were 32 cm in diameter.
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