Tunnel profile introduction: There are passages underground under the castle, extending in all directions inside the castle, forming an underground military defense facility. The tunnel is three-dimensional, with the upper level more than one meter above the ground, the middle level eight to ten meters above the ground, and the bottom level seventeen to twenty meters above the ground, each about two meters high. It bends and blurs to form a network structure. There are holes in the ditches on the north and south sides of the fort, which can be used as entrances and exits as well as sentry posts.