The Tianmenshan Natural Scenic Area is located in Liukeyu Village, Shicheng Town, Miyun County, Beijing. The scenic area is 4 kilometers long, covering an area of 3000 mu, with more than 40 scenic spots. The main scene "Tianmen" is also known as "扁dan eye", with an altitude of more than 800 meters, a height of 60 meters, and a width of 35 meters. It is said that it was the "扁dan eye" used by Erlang Shen to carry mountains to fill the sea. Erlang Shen was carrying mountains when he saw that the扁dan eye was about to split, so he put down the mountain. The southern "扁dan eye" is in Zhangjiajie, Hunan, while the northern one is in Liukeyu Village. This cave is embedded in the sheer cliff, open and transparent, like a city gate leading to the celestial court, hence the name Tianmenshan. Because it is in the north, people call it "Beitiamenshan".