Non Nuoc Cao Bang covers more than 3,000 sq.km. spreading over 9 districts. The limestone terrain contains Thang Hen lake, Phia Oac-Phia Den National Park, Ban Gioc waterfall, Pac Bo cave, and Lenin stream. Photo: Hachi.

Ban Gioc waterfall in Trung Khanh district is the most magnificent waterfall in Vietnam. Its waters fall down 30 meters of limestone. (Photo: Tran Phuong)

The best time to visit Cao Bang is between September and December, when Ban Gioc waterfall is filled with clear water. (Photo: Huu Thong)
Phia Oac-Phia Den National Park has a complex terrain characterized by narrow valleys between high, steep mountains with a slope of more than 38 degrees. Many of the mountains are 1000m-2000m high. Phia Oac, for example, is 1935m and Phia Den is 1391m. (Photo: Caobanggeopark)

The mountains caught the attention of the French at the beginning of the 20th century. They spent holidays amid the natural beauty of Phia Oac-Phia Den. (Photo: Caobanggeopark)

The Cao Vit gibbon conservation area in Phong Nam, Ngoc Con, and Ngoc Khe communes of Trung Khanh district has an area of 7,600 ha, 1,600 ha of which is primary or secondary forest. (Photo: VNA)
An adult Cao Vit gibbon has long arms and weighs 7-8 kg. The male is black and has a crest of fur on its crown. An adult female is yellow with black spots and has no crest. A baby gibbon is yellow. (Photo: VNA)

Thang Hen lake is in Tra Linh district, 30 km from Cao Bang city. Its name in the Tay language means ‘bee sting’ because it looks from above like a bee’s stinger.
The Thang Hen complex includes 36 natural lakes, all of them connected by underground caves. The 36 lakes lie in a huge valley abutting Quoc Toan (Tra Linh) and Ngu Lao (Hoa An) commune. (Photo: Caobangtv)
The clear green water of the Thang Hen complex
Ky Rang cave is 1.5 km from Thang Hen beneath Ky Rang mountain. The cave is 417m long and 34m tall. The widest part is 30m and the narrowest just 0.7m. It contains 2 big rooms separated by narrow doors and slopes. It has a magnificent stalactite system. (Photo: Evan)

The Pac Bo historical relic is in Ha Quang district, 50 km north of Cao Bang city. President Ho Chi Minh stayed in the Coc Bo cave here when he returned to Vietnam in 1941 to lead a revolution against the French. Pac Bo means ‘source’. (Photo: TL)

Lenin stream in Pac Bo has blue-green water and is surrounded by a forest. President Ho Chi Minh once worked and fished here. (Photo: Tue Minh)