Introduction to the One-line Sky: The One-line Sky is an artificial excavation and is the Shimen Fortress. When you are in it, between the two cliffs, it is like a line of sky, which is eerie. There are flying rocks above and the Changshou River below. On the left Based on the ancient castle, and later on the ruins of the Goryeo camp, there is a strong trend of "one man can guard the gate, and ten thousand men cannot open it".