Introduction to Yansai Lake: Yansai Lake is located 3.5 kilometers west of Shanhaiguan City. It is named after its location in Yanshan Fortress. The vast lake area of ​​15 square kilometers is like a painting: the cliffs and mountains on both sides reflect the green and crystal clear lake center; the rugged rocks on the cliffside are like a stone forest scenery, which makes people overwhelmed. Birdsong Forest is located in Yansai Lake Scenic Area. There are more than 100 species of rare birds. Yansai Lake is the first artificial lake starting from the east of the Great Wall.