In Vietnam’s Quang Binh province lies the Hang Son Doong Cave, the largest cave in the world stretching more than five kilometers long and reaching heights of 200 meters! It was first discovered in 1991, when a local farmer stumbled across it and sought shelter from a storm. Before that it had remained undetected beneath the Annamite Mountains for 3 million years!

Awesome capture by Elinna Yao.
https://www.instagram.com/elinna.yao/