Oak Ridge, Tenn.
Oak Ridge didn't exist until the federal government evicted the area's rural residents in 1942, and the city didn't appear on a map until after World War II. Known as the "Secret City," it was established as one of three sites for developing materials for the Manhattan Project, and its residents lived a life of secrecy. The entire city was gated, the homes had no addresses, and the workers weren't told what they were working on. Today, Oak Ridge is still home to four secret military facilities, which U.S. citizens can tour one day only during the annual Secret City Festival. In addition to these one-of-a-kind tours, the city is also home to the American Museum of Science & Energy and the International Friendship Bell, the first monument between a U.S. Manhattan Project city and Japan.