Introduction to the old site of the South Gate Guards Station: The old site of the South Gate Guards Station is the only existing guard station. The bacteria laboratory and production base of the 731 unit are set up in the camp area, with separate security facilities and an earth wall 5 kilometers long, 2.5 meters high and 1 meter wide. There is a high-voltage power grid on the wall, a moat is dug outside the wall, and there are five guard posts along the earthen wall. It is the main passage for Japanese people to enter and exit the headquarters building, bacterial laboratory, and production base.