Introduction to the air-raid shelter: The "air-raid shelter" is located 100 meters north of the lower west gate of the ancient city. There is a hidden hole on the inside of the rammed earth wall, more than 1 meter above the ground, with bricks inside and earth outside, two or three meters down the hole. , the "air raid shelter" runs in the north-south direction along the wall, about 150 meters to the south and more than 200 meters to the north. The hole is about 2 meters high and varies in width. The holes are all made of bricks. There are also many side holes in the "air raid shelter", with earthen kangs etc. built inside.