Hiroshima is known as the first city in history to be destroyed by a nuclear weapon. On Aug. 6, 1945, the U.S. Air Force dropped an atomic bomb known as "Little Boy" onto the city, destroying almost 5 square miles of Hiroshima and killing 30 percent of the city's population. Today, tourists can learn about the bomb's terrible impact at the Hiroshima Peace Site, which is home to the Hiroshima Peace Memorial Museum and the Atomic Bomb Dome (pictured). Constructed in 1915 as a commercial building, the domed building was gutted by the bomb, and all the people inside it died instantly. Today the dome is a United Nations World Heritage Site and serves as a symbol for the abolition of nuclear weapons and a reminder of the devastation the bomb caused.