Morning, driver will escort you about 200km from Hue to the Son River in Quang Binh province, where you take a boat trip to the famed caves at Phong Nha – Ke Bang National Park. The Park is one of the world's two largest limestone regions. In comparison with 41 other world heritage sites which have karsts, Phong Nha has dissimilar geomorphic, geologic and biotic conditions. The karsts of Phong Nha can be traced back to Palaeozoic 400 million years ago. This makes Phong Nha is the oldest major karst in Asia. The area has numerous grottoes and caves. Vietnamese and British scientists have so far surveyed a total of 20 caves with a total length of 70 km. Of these surveyed caves, 17 were in the Phong Nha area and three in the Ke Bang area. Following the narrow underground river, you explore the most impressive Phong Nha cave, from which the name to the whole system. The Cave is famous for its rock formation which have been given names such as the "Lion", the "Fairy Caves", the "Royal Court", and the "Buddha". Afterwards, you return to Dong Hoi for lunch before driving back to Hue.