Subterranean Cities

“In certain parts of the world, the ground is honeycombed with secret man-made tunnels and rooms. Many of these remain secret from the general public, some of them supposedly containing what amounts to a self-contained city, including electricity production, water purification, food storage, restaurants, and living quarters for thousands of people. Even some entire factories have been housed underground, to protect them from bombings during wartime. A number of the subterranean bases are World War 2 and Cold War relics, long abandoned by the governments which tunneled them out.”