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In 2009 surveyors found 20 new caves in the park with a combined length of 56 km (35 miles).
Cave explorers from the British Caving Association made the survey in April 2009, in the park and the adjacent areas. The new caves included Son Doong, whose main chamber is more than 5 km long, 200 m high and 150 m wide. The survey gave the park the numbers that now appear in its description.
Source: Wikipedia, Phong Nha-Ke Bang National Park. Checked October 2026.
A local man named Ho Khanh found the entrance to Son Doong on 10 December 1990. British cavers surveyed it in 2009.
Ho Khanh found the entrance while searching for agarwood, a valuable timber. The sound of rushing water and the strong wind coming out of the entrance discouraged him, and he later forgot where it was. After he mentioned it to two British cave researchers, he managed to rediscover the entrance in 2008.
Source: Wikipedia, Hang Son Doong. Checked October 2026.
In early August 2013 a tourist group explored Son Doong on a guided tour that cost US$3,000 each.
Permits are required and are made available on a limited basis, from January to August. After August, heavy rains raise the river levels and make the cave largely inaccessible. The source says that Oxalis Adventure Tours has held the permission to enter for tourism since 2017, so plan well ahead.
As of 2013. Source: Wikipedia, Hang Son Doong. Checked October 2026.
The core zone of Phong Nha-Ke Bang National Park covers 857.54 square km (331 square miles).
The park is in central Quang Tri Province, about 500 km south of Hanoi, and it borders Hin Namno National Park in Laos to the west. Before it became a national park it was a nature reserve, declared by the government in 1986. The Prime Minister converted it into a national park in 2001 to protect forest resources and biodiversity.
Source: Wikipedia, Phong Nha-Ke Bang National Park. Checked October 2026.
The park holds about 300 caves and grottoes. A 2009 survey put the total discovered length of the cave system at about 126 km (78 miles).
The figure covers just what has been discovered: the source says many areas are still not well explored, so the real total may be higher. The 2009 survey was carried out by British and Vietnamese explorers, and it is the same one that found Son Doong Cave.
Source: Wikipedia, Phong Nha-Ke Bang National Park. Checked October 2026.
Son Doong Cave is more than 5 km (3.1 miles) long, about 200 m (660 ft) high and 150 m (490 ft) wide.
These dimensions are for the main passage. The whole cave runs for about 9 km and is punctuated by two large dolines, where the ceiling has collapsed. They let sunlight in, so trees and other vegetation grow inside. The 2009 expedition was stopped at one point by a 60 m flowstone wall that it named the Great Wall of Vietnam.
Source: Wikipedia, Hang Son Doong. Checked October 2026.
A British Cave Research Association survey in April 2009 put the volume of Son Doong at 38,500,000 cubic metres.
The expedition ran from 10 to 14 April 2009. A 60 m flowstone wall stopped its progress, and the team returned in March 2010, traversed the wall and reached the end of the passage. They estimated that the overall length of the cave system exceeded 9 km, longer than the main passage alone.
Source: Wikipedia, Hang Son Doong. Checked October 2026.
The limestone karst here has been developing since the Paleozoic era, some 400 million years ago.
As many as seven different major levels of karst development have occurred here as a result of tectonic uplift and changing sea levels, which makes the landscape extremely complex. There is also strong evidence that sulphurous solution and hydrothermal action played an important role in shaping the broad-scale landscape and the caves.
Source: Wikipedia, Phong Nha-Ke Bang National Park. Checked October 2026.
Some stalagmites inside Son Doong grow up to 80 m (260 ft) tall, and two collapsed ceilings let jungle grow inside the cave.
Behind the Great Wall of Vietnam the explorers found cave pearls the size of baseballs, an abnormally large size. The source describes the interior as so large that an entire New York block, skyscrapers included, could fit inside, or that a Boeing 747 could fly through without its wings touching either side.
Source: Wikipedia, Hang Son Doong. Checked October 2026.
Climate, airports and UNESCO status for Phong Nha are on its destination page. More places are on the fun facts index.