The largest cave passage on Earth, and it is not close. Over 9 km long, around 200 metres high and 150 metres wide, roughly 38.5 million cubic metres of space, with a river running through the bottom of it, stalagmites up to 80 metres tall and cave pearls the size that make people ask if they are real. Two dolines, places where the ceiling has fallen in, let enough light down that there is actual jungle growing inside the cave. Hồ Khanh found the entrance on 10 December 1990 while looking for agarwood, lost it again, and found it a second time in 2008; the British Cave Research Association surveyed it in April 2009 and finished in March 2010. Access is tightly held: permits are limited, one licensed operator runs the expedition, and it is closed September to December while the water comes up and the place recovers. Phong Nha-Kẻ Bàng National Park.
Vietnam
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