[The World's 20 Most Amazing Tunnels]Cu Chi Tunnels, Vietnam

 

 

Built as hiding spots for Viet Cong guerillas, the three-story-deep Cu Chi tunnels near Ho Chi Minh City are part of a vast tunnel network that lies under much of the country. Once a tool used against the U.S. in wartime, they’re now a tourist attraction that draws thousands every year. (Tyler Strause/flickr.com)