|Thang Hen Lake was a fresh water lake lying in the community of 36 fresh water lakes on the high mountain of Tra Linh District. It is around 3,000 metres long, more than 1,000 metres wide, and thousands of metres above the sea level. The landscape here is quite charming with lines of green trees beside the precarious cliffs, reflecting on the pure water surface and meandering around the underground rock peaks. In the morning, taking a look at the lake from the top of the mountain, people can see masses of cloud like silky cloths flying in the wind. At the head of the lake Thang Hen, there is a wide cave and water in this cave flows out constantly, making the scenery more imposing. Everyday, there are two turns of tide: one up and one down, at Thanh Hen Lake. Even in the flood season or droughty season, the water in this lake still stays green and pure.
The legend about Thang Hen Lake is an interesting discovery to travelers. According to the folks, a very long time ago, in Tra Linh area, there is a handsome and intelligent young man. He passed the national examination (in the old time), became a mandarin and was awarded seven days for returning his village after achieving such honour and entering the imperial city. Before he went to the imperial city, he met and married a beautiful lady, Bi Ooc. Because of spending time with his newly-married wife, he forgot the time to depart to the capital city. Until the seventh night, he suddenly remembered about this business, said goodbye to his wife and parents and hurriedly ran to the imperial city.
Passing 36 valleys among rocky mountains in the midnight, he dropped with fatigue and unexpectedly smashed into the mountain and died. Those 36 valleys today are 36 small and large lakes with various names in the forest and mountainous region in Tra Linh District. It is believed that the place that young man died is now the locality of Thang Hen Lake.
Nowadays, at Thang Hen Lake area, people have built boarding-houses and hotels and this place now is getting much attention and development focus from the provincial authorities with purpose to make it become an ideal location for ecological tourism and resting for both domestic and foreign tourists. In 2002, Thang Hen Lake was recognised as an ecological tourism area of Cao Bang Province by the Ministry of Culture and Information.