Hang Son Doong was discovered in 2009 by a British-Vietnamese team of scientists and speleologists. Local people had known about the passage at least since 1991 but they did not dare to access such a unique and mysterious place without necessary equipment. Difficult access and deafening noise of the river used to protect Hang Son Doong against any curious visitors until 2009. During the first expedition in the spring 2009, the team explored two and a half miles of the cave but then a wall of muddy calcite stopped them. They named it the Great Wall of Vietnam. A year later, they came back to explore the remaining part of the passage.
Hang Son Doong is the largest cave in the world. It is believed to be nearly twice the size of the current record holder. It is 200 meters high, 150 meters wide, more than 6.5 km long and it is located below another cave. There is a jungle inside this mammoth cavern. Hang Son Doong is hard to access. The nearest populated locality is about 10 km far from the cave. In 2009, the explorers had to spend six hours trekking through the jungle to reach the cave.
There is a lake inside Hang Son Doong. In 2009, the scientists - explorers were not able to measure its depth so this is one of the tasks for future expeditions.
Hang Son Doong has not been made accessible to visitors yet. According to the British Speleological Association, it would be very wrong to open such a unique natural monument to the public.