Explore Than Than Mountain, Cao Bang Than Mat Mountain (Thung Mountain) is located in Quoc Toan commune, Tra Linh district in the complex of 36 Thang Hen lakes, a prominent destination of Cao Bang geopark. This mountain is also known by another name "Perforation Mountain", due to the external shape of the mountain, at the top there is a circular cave like the "eye" of the mountain with a diameter of more than 50m. is a mountain considered "unique" in Vietnam.