Which country has the world's largest cave, Son Doong?

Son Doong Cave is in Vietnam, making Vietnam the answer to the question about the country with the world’s largest cave. The cave lies in Phong Nha–Kẻ Bàng National Park near the Laos border.

Son Doong is regarded as the world’s largest natural cave by passage volume. Its main passage is about 9 kilometres long, more than 200 metres high and roughly 150 metres wide. Collapsed sections of the roof, called dolines, allow sunlight and rainforest vegetation to grow inside the cavern.

Local man Hồ Khanh found the entrance in 1990 while searching for forest products. British and Vietnamese cave explorers surveyed it in 2009, bringing its extraordinary scale to international attention. The cave formed in limestone roughly 2–5 million years ago and contains an underground river.

A common mix-up is confusing the world’s largest cave with the world’s longest cave. Son Doong holds the size-by-volume distinction; other caves may lead in total mapped length or depth.