Dug deep into the earth, the tunnels have long been an enduring source of fascination for visitors seeking to learn more about the war that ravaged Vietnam during the 1960s and 1970s.

Located some 70 kilometres from downtown Ho Chi Minh City, the tunnels served as living quarters and weapon stores of Vietnamese soldiers during the wartime.

Despite repeated attempts by the enemy to destroy the tunnels, they survived and are now maintained as memorials by the Vietnamese Government, CNN wrote.

The tunnel system runs in a zig-zag shape underground, with the main route branching out in multiple directions that connect together in certain areas, depending on the terrain.

✃ Some tunnels have structures that include two to three floors. Stairs between floors have trap-doors that lead to secret vaults.

Other tunnels on the CNN list include Tokyo Bay Aqua-line (Japan), Bund Sightseeing Tunnel (China), Glow Worm Tunnel (Australia), and Gotthard Base Tunnel (Switzerland)./.