Discover one of Cao Bang's most unique natural landmarks, Nui Thung Mountain, often nicknamed Angel Eye Mountain. Located in a scenic valley near Thang Hen Lake, this karst mountain features a large, perfectly round hole piercing right through its peak, creating a stunning and unusual sight.

The valley floor around the mountain changes seasonally, sometimes filling with water to form Nam Tra Lake (rainy season) or becoming a grassy pasture (dry season). Visiting Angel Eye Mountain offers incredible photo opportunities and a sense of discovering a hidden gem within the Cao Bang Geopark.