Cu Chi tunnels.

We visited the Cu Chi tunnels about 100 km from Ho Chi Minh City. During the Vietnam war some of the Viet Cong guerillas lived underground here. They dug hundreds of miles of tunnels over a 20 year period. They laid some horrendous booby traps in the region (which would not look out of place in any torture chamber ). The US were equally bad with indiscriminate bombings and chemical weapons. A truly awful war.
This photo is of one of the well hidden tunnel entrances