The Chu Chi Tunnels are part of a massive war museum in Ho Chi Minh. They offer visitors a sneak-peek at the underground life of Vietnamese soldiers back in 1948. The site has over 120km of underground tunnels, with trapdoors, living areas, kitchens, storage facilities, armoury, hospitals, and command centres. After the war against the French, Vietnamese soldiers expanded the tunnels and included effective air filtration systems, which helped them survive the Chu Chi carpet-bombings.
It is now one of Ho Chi Minh’s most iconic attractions. You can enjoy plenty of activities during your visit. A popular option is following the narrow routes of the underground tunnel. Before entering the underground tunnels, visitors watch a short film of Chu Chi Tunnels so that they understand how the tunnel system works. Parts of Chu Chi Tunnels are also cemented and widened so that the crawl is less harrowing than it would have been in the past.
http://www.vietnam-guide.com/ho-chi-minh-city/cu-chi-tunnels.htm