Introduction to the city wall ruins: The city wall of Wunu Mountain City is 4,754 meters long and is divided into two parts: natural walls and artificial walls, with natural walls accounting for the majority. The artificial walls of the mountain city are all made of stone, with one to five layers of large stone strips as the wall base, with wedge-shaped stones laid flat on them, spindle-shaped stones inserted into the inner wall, and filled with gravel and stones. The mountain fortress pioneered the Goguryeo nation in terms of wall masonry and wall stone processing, and had a huge impact on later Goguryeo mountain fortress architecture and even Northeast Asian construction technology.