The largest cave in the world is called Dong Soo found in the Vietnamese National Park. The Vietnamese National Park is located in Phong Na-Khe Bang.
Dong Soo is hidden under a large forest, which makes it almost inaccessible. It is 4.5 km long and 80 meters high, and has towering limestone stalagmites.
The Phong Na-Khe Bang National Park is a UNESCO heritage site. It is rich in caves, and is located 50 km north of Dong Hoi, the nearest town with an airport; and 500km from Hanoi.
The tour operator, Trails in the World, offers a package in this area of northern Vietnam. Tourists can embark on a 14-day journey beyond the tourist circuits; trekking with visits to the valleys and picturesque villages that are home to ethnic minorities; and then visit the Phong Na-Khe Bang park on foot and by bicycle.
If you prefer to rely on a local tour operator, the trip can be a bit more adventurous in the local traditions The Planks, based in Hanoi, offers a package that costs the equivalent of 20% less with the added opportunity to visit the caves of Park in a kayak. Among other things, The Planks also provides excursions to discover the life in the countryside, visiting markets and monuments of the city’s most traditional, and short cruises in the bay where the film “Indochina” was shot.