Hang En is one of the largest natural caves in the world. It is 1.6km long with a huge exit and entrance that allows enough light to ensure that the cave is never completely dark during daylight. The largest opening is 120m high and 140m across, though some chambers are as wide as 180m. To put things into perspective, the length of a soccer field is 110m and New York’s Statue of Liberty is just over 90m.
The karst in Phong Nha-Ke Bang National park is 400-450 million years old but Hang En probably only dates back 3 million years. Every wet season the Rao Thuong floods to inconceivable heights, constantly eroding more of the limestone away as the cave continues to grow.