Phong Nha means “Cave of Teeth” is the underwater cave. A team of British divers explored 35km of the cave and made the first reliable map of Phong Nha with main cave system is nearly 8km long. However, visitors can only access less than 1,5km. Stalactites and stalagmites jut out like strange trees, exciting visitors’ imaginations. In the mountain side right above Phong Nha cave, there’s also a dry cave called Tien Son. Like Phong Nha cave, this cave features spectacular stalactites and stalagmites shaped like several fairy-tales. Stalactite and stalagmite columns and walls here create strange sounds like that of gong and drum if they are knocked with the hand.

In November and December, the river is prone to flooding. Therefore, the underground cave may be closed, though it’s possible but it also may be dangerous to visit the cave.