The Cu Chi Tunnels, built by Vietnamese freedom fighters as shelter from US bombs and troops during the Vietnam War, has been chosen by CNN as one of world’s top underground tourist attractions.

The tunnels were used as living quarters, hospitals, supply routes and storage areas.

Vietnamese freedom fighters also used the tunnels to hide, travel undetected, establish booby traps and launch ambushes. A tank was even found in one of the tunnels, according to CNN.

This 120-kilometer-long tunnel complex, part of a much larger network throughout the country, now operates as a war memorial and visitors - at least those who can squeeze through the tiny trapdoors - can explore several of the tunnels.

The list of 12 of the world's best subterranean sights compiled by CNN also includes the G-Can flood surge tunnels in Tokyo, Japan, and the Shanghai Tunnels in Portland, Oregon, United States.

Only 60km from the center of Ho Chi Minh City, the Cu Chi Tunnels are one of the city’s most important historical tourist attractions.

More than 120 kilometers of the original complex, built between 1946 and 1948, by Cu Chi District residents have been preserved for tourists to view.

In 1965, once the US invaded Vietnam, the system was expanded, with three different layers and a total length of 200km.

The top, middle and bottom layers were 3m, 6m and 12m from the ground surface, but they were quite airy.

The construction was done in two sections – Ben Dinh in Nhuan Duc communes, which was the base of the district Party committee between 1960 and 1975, and Ben Duoc, which was the Saigon-Gia Dinh military zone or the Saigon base of the Liberation Army.

Visitors are allowed to crawl into the tunnels at Ben Dinh.

Twenty kilometers away at Ben Duoc in Phu Hiep Hamlet in Phu My Hung Commune, visitors can enter a temple where dead soldiers are worshipped.

Above the tunnel system, ramparts, mine fields and bamboo-stake pits served as defenses in the guerilla war.

Cu Chi people also built a system of trenches for traveling and fighting around the underground openings.