Tien Son cave is another beautiful cave in Phong Nha-Ke Bang area. Tien Son cave was created tens of millions years ago when water current holed this limestone mount in Ke Bang.
Tien Son cave was discovered by a local inhabitant by accident in 1935. It is located in Son Trach Commune, Bố Trạch District. The entry mouth of Tien Son is 1 km from Phong Nha cave, at an altitude of 200 m. This cave is 980 m in length. A 10 m deep hole is situated 400 m from the entry mouth, then a 500 m long underground cave, dangerous for tourists and therefore is open to professional expeditionists only. 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. According to British cave scientists; Tien Son cave was created tens of millions years ago when water current holed this limestone mount in Ke Bang. Following a series of landforms and movement of rocks, this mass was levered or lowered, blocking the current and creating what is now Tien Son cave while the underground river redirected its current to Phong Nha cave. Although Phong Nha and Tien Son caves are located next to each other, there are no linking grottos between them.