The Cu Chi Tunnels are an immense network of connecting underground tunnels located about 40 km northwest of Ho Chi Minh City (Saigon). The tunnels were used by Viet Cong guerrillas as hiding spots during the Vietnam War, and were the base of operations for the Tết Offensive in 1968. The tunnels have become a popular tourist attraction, and visitors are invited to crawl around in the safer parts of the tunnel system.