Phong Nha - Ke Bang National Park is located in the territories of communes ((Vietnamese): xã): Tan Trach, Thuong Trach, Phuc Trach, Xuan Trach and Son Trach of Bo Trach district and a small part of Minh Hoa district in the center of Quang Binh province, around 40 km north-west of the provincial capital city of Dong Hoi. The park is bordered by Hin Namno karst area of Khammouan Province of Laos in the west. The road distances are about 500 km south of the capital Hanoi and 260 km north of the port city of Da Nang. The geographical coordinates are 17°32′14″N, 106°9′4.5″E.

The park is situated around 30 km west of South China Sea and National Road 1A, near Ho Chi Minh Highway and 28 km west of Hanoi-Saigon Railway and is accessed by road or waterway by boat through the estuary in South China Sea upwards. There is a small airport near the park accessible by helicopter or small aircraft (Khe Giat Airbase), an airbase used by North Vietnamese Airforce during Vietnam War, notably in the Battle of Dong Hoi.

The Phong Nha–Ke Bang karst has evolved since the PaleozoicPalaeozoic (some 400 million years ago) and so is the oldest major karst area in Asia. It has been subject to massive tectonic changes, and comprises a series of rock types that are interbedded in complex ways. Probably as many as seven different major levels of karst development have occurred as a result of tectonic uplift and changing sea levels, thus the karst landscape of PNKB is extremely complex with high geodiversity and many geomorphic features of considerable significance. Like much of Vietnam, it has been subject to extensive tectonic change, and so the limestones of Phong Nha are inter-bedded with a number of other rocks. There is also strong evidence that sulphurous solution and hydrothermal action have played an important role in shaping the broad-scale landscape and the caves, though this has not yet been properly assessed.

Phong Nha-Ke Bang National 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 era, 400 million years ago. This makes Phong Nha the oldest major karst in Asia. If the Hin Namno, bordering Phong Nha on the west (in Laotian territory) was to be combined with the national park in a continuous reserve, the combined reserve would be the largest surviving karst forest in South-east Asia (317,754 ha).

In general, there are two groups of landforms in the Phong Nha - Kẻ Bàng area, namely non-karstic and karstic landforms. Non-karstic landforms includes three types: The middle and low dome-block mountains developed in intrusive magmatic massifs; The middle denudation-structural mountain belts developed in terrigenous rocks of Cretaceous age; and The low block-denudational mountain belts developed in other terrigenous rocks.

Karstic landforms in this area are of typical tropical karst which are divided into two groups of forms: The karstic forms on the surface including cone and tower karst, karrens, valleys and dolines, border polje, etc; The underground karst consisting of caves.

Phong Nha - Ke Bang also contains two dozens of mountain peaks with over 1,000 metres height. Noteworthy peaks are the Peak Co Rilata with ta height of 1,128 m and the Peak Co Preu with a height of 1,213 m.

Mounts in karstic area of the park rise at typical height of above 800 m constitute a continous range along Laotian-Vietnamese borderline, of which notable summits above 1000 m are: Phu Tạo (1174m), Co Unet (1150m), Phu Canh (1095m), Phu Mun (1078m), Phu Tu En (1078m), Phu On Chinh (1068m), Phu Dung (1064m), Phu Tu Ôc (1053m), Phu Long (1015m), Phu Ôc (1015m), Phu Dong (1002m). Inserting into these summits are 800-1000 m high summits of Phu Sinh (965m), Phu Co Tri (949m), Phu On Boi (933m), Phu Tu (956m), Phu Toan (905m), Phu Phong (902m), núi Ma Ma (835m).

Phong Nha-Ke Bang covers 300 different grottoes and caves. Phong Nha cave is assesed by BCRA as the top cave in the world due to its 4 top records: the longest underground river, the highest and longest cave, broadest and most beautiful fine sand beaches inside the caves, the most spectacular stalagmites and stalactites.According to the assessment of UNESCO, The karst formation of Phong Nha-Ke Bang National Park has evolved since the Palaeozoic (some 400 million years ago) and so is the oldest major karst area in Asia and Phong Nha displays an impressive amount of evidence of earth’s history. It is a site of very great importance for increasing our understanding of the geologic, geomorphic and geo-chronological history of the region.