Introduction to the underground fortifications: It is 17 meters deep from the ground, with a total construction area of more than 10,000 square meters. It is made of reinforced concrete and consists of a main road and multiple branch roads, with a total length of about 4,000 meters. , there are more than 50 rooms of different sizes and uses on both sides of the passage, which are equipped with headquarters, headquarters, hospitals, telecommunications rooms, kitchens, soldiers' dormitories, shooting holes and bunkers, ventilation holes, toilets, etc., which is called For "underground city".