SON DOONG CAVES

In Vietnamese it means " Mountain River Cave". It is located near the Laos-Vietnam border The local men were afraid of the cave for the whistling sound caused by an underground river. It was not until 2009 that it became public knowledge, after a group of scientists from the British Cave Research Association, led by Howard and Deb Limbert, conducted a survey in April, 2009.
" I thought this would be an amazing place to visit. The Son Doong is the world's largest cave, created 2-5 million years ago. A half-mile block of 40-story buildings could fit inside it."