A vast cave hideout used during the Vietnam War has opened to the public in the mountains of northern Laos. Nearly 500 caves served as a virtual city to 23,000 refugees, equipped with shops, schools, a hospital and printing press. After the war, the site was used as a political reeducation camp. Now it’s set to follow in the footsteps of the 75-mile Cu Chi tunnels, one of southern Vietnam’s most popular tourist attractions.