Hang Son Doong and other caves of the Phong Nha-Kẻ Bàng karst, Quảng Bình Province, Vietnam

Abstract The dense tropical rainforest of Phong Nha-Kẻ Bang National Park harbors part of the most extensive karst landscape in southeast Asia. Located within the karst are giant river caves that drain the Kẻ Bang massif where over 300 caves have been documented so far. Hang Son Doong (Mountain River Cave) is a segment of one of the cave systems that drains the massif and contains the largest-dimension cave passage in the world. Hang Khe Ry, located upstream of Hang Son Doong is among the longest river caves in the world and both are segments of the Phong Nha drainage system which runs from the southern end of the national park near the Laos border northeast to the Hang Phong Nha resurgence on the Son River (song Troc). The core of PNKB National Park covers 857.54 km2 with a buffer zone that includes 1954 km2 created to protect one of the world's largest karst regions as well as the ecosystem of the limestone forest of the Annamite Mountain Range.