They're called the Cu Chi Tunnels, and tourists travel from around the world to crawl inside. They love ducking below camouflage trap doors and cramming themselves in the tight passageways.

Inside, the tunnel rats faced danger at every corner, and they had to watch out for ambushes, booby traps ... Chi Minh City, formally known as Saigon, I arrived at Ben Duoc Tunnels, one of the two ...

Many weapons, including booby traps and mines ... This map gives an idea of the extent of the tunnel system at Cu Chi--the orange lines represent major tunnels ...