The suburban Cu Chi district of Ho Chi Minh City sits atop an enormous network of tunnels. For thousands of Viet Cong soldiers, this sprawling network of cramped passageways was an entire world unto itself, complete with living quarters, communications centers and hospitals.

Though the tunnels became famous in the Vietnam War, parts of the network were first constructed in the 1940s by peasants fighting French occupation forces. By the mid-1960s, the tunnel system had grown to over 75 miles in length. Viet Cong soldiers living in the tunnels would spend most of their day digging new passageways, only daring to venture out at night for supplies and to perform guerilla raids. Defensive measures built into the network included explosive booby traps and stake pits, making the work of American soldiers attempting to infiltrate the tunnels incredibly dangerous.

Beyond the intentional deterrents, the tunnels were also hot, damp and infested with a variety of snakes and insects; reports suggest that as many as half of all Viet Cong soldiers were infected with malaria at any given time.

American bombing raids succeeded in destroying sections of the tunnel network near the end of the war, but much of the system remains intact. It has since become a tourist attraction, where visitors can attempt to crawl through a short passage - or, if necessary, a section that has been widened for the convenience of westerners.