The Phong Nha Cave, from which the name to the whole system and the park is derived, is famous for its rock formations which have been given names such as the “Lion”, the “Fairy Caves”, the “Royal Court”, and the “Buddha”. This cave is 7729 m long, contains 14 grottos, with a 13,969 m-long underground river. The scientists have surveyed 44.5 km of grottos in this cave so far, but tourists can only penetrate to a distance of 1500 m.
Phong Nha Cave, like most of the caves in this area, has been continuously shaped by the Chay River. As one gets farther into the cave, the more illusory the stalactites and stalagmites look as they glitter when bright light is shone on them. The Son River flows into the mouth of the cave and keeps flowing underground, where it is referred to as the Nam Aki River, then this river emerges at a site 20 km to the south near Pu Pha Dam Mountain.
The main Phong Nha cave includes 14 chambers, connected by an underwater river that runs for 1.5 km. Secondary corridors branch off in all directions. The Outer Cave and some of the Inner Caves have roofs that tower between 25 and 40 meters above the water level.
From the 14th chamber there may be other corridors leading to similarly large chambers, but this area proves more dangerous for explorers because of the ongoing erosion of the limestone of the cavern. The Shallow Cave is located 800 meters from the cave mouth, where there is a spectacular landscape of sand and rock. Stalactites and stalagmites jut out like strange trees, exciting visitor’s imaginations.