Thang Hen Lake (commonly known as Thang Hen), located in Tra Linh commune, more than 30 km east of Cao Bang city center, was recognized as a national scenic spot in 2001.

The Thang Hen lake complex consists of 36 natural lakes situated in a large valley, interconnected by a system of caves and underground rivers and caves. Among them, Thang Hen Lake is the largest, nearly 2 km long, surrounded by ancient forests interspersed with jagged rock formations. In the local language, Thang Hen means "water-retaining lake," because the lake never dries up, even during the dry season, while neighboring lakes only have water during the rainy season.