The Viet Cong built an extensive networks of tunnels in the area north of Saigon known during the war as the Iron Triangle. This was the approach to Saigon for the VC and the North Vietnamese, and South Vietnam and the US set up a major defense here.
The tunnels consisted not only of tunnels to get from one area to another, but also of rooms for just about every purpose – communication, sleeping, hospitals, cooking . . . even occasionally theater. The VC actually lived in these tunnels for years. Children were born here, villagers and others took refuge here. Women were guides and fighters. There was a whole society in the tunnels. There was an elaborate ventilation system, and trap doors that could be closed to protect the lower levels from bomb or gas attacks.