The U.S. military dropped the first atomic bomb in world history in Hiroshima, Japan on August 6, 1945. The bomb instantly killed thousands, with a total casualty count of 140,000 people. A once-thriving metropolis, Hiroshima was flattened by the bomb except for a few buildings -- one of them the domed Hiroshima Prefectural Commercial Exhibition Hall. The Hall retained some of its walls and the steel frame of the dome; this structure quickly became a symbol of survival and rebuilding. The building is now known as the A-bomb Dome and is the main attraction at Hiroshima Peace Memorial Park. The domed building was intentionally left in its original condition to remind visitors of the effects of nuclear war. The building is particularly striking at night, when an eerie green glow washes the outer walls of the frame and a red light emits from inside to signify the atom bomb and those lost to it.