The rocky pinnacles jutting above the otherwise flat jungle landscape hide a multitude of underground caves and rivers. These limestone karst formations are among the oldest and largest in Asia, and the region’s more than 78 inches of warm annual rainfall have eroded them into some spectacular formations. Phong Nha Cave, the most popular at an impressive 27 miles long, is the most popular. Accessed by covered boats via a river running through its entrance, visitors can explore the first half-mile or so. Its cavernous entryway—165 feet at its tallest point, and its most impressive features including a massive stalactite wall known as Hermit’s Hair, are illuminated by garish colored lights.
Also in Phong Nha Cave, as well as the mountainside Tien Son dry cave accessed by a steep staircase, are mysterious and still un-deciphered writings believed to have been left by Cham merchants who likely lived here between the 2nd and 10th centuries. More caves throughout Phong Nha-Ke Bang National Park—including the only recently discovered Hang Son Doong—are being opened to the public via fairly expensive private multi-day caving tours every year. The entire 330-square-mile area was inscribed as a UNESCO World Heritage site in 2003.
Because the Phong Nha Caves are centrally located, longer tours departing from Hue, Ho Ci Min City and even Hanoi stop here. Shorter regional day trip jaunts depart from Dong Hoi, 40 miles east and along the coast. Several guesthouses in the area also make it possible for deeper exploration of the area. Many organized Phong Nha cave tours include entrance fees. Note that hiking in the national park is possible only with a licensed guide, as the area still conceals unexploded ordnance from the war.