The Hiroshima Peace Memorial Museum is a museum in Japan dedicated to documenting the atomic bombing of Hiroshima in World War II. It made its only appearance in the Season Thirteen episode, "Whale Whores".
Emperor Akihito takes Cartman, Stan, and Kenny to a tour of the museum, explaining the bombing of Hiroshima. He explains that the bombing caused the death and suffering of many Japanese alike. He then explains that the Americans gave a picture of a dolphin and a whale flying the Enola Gay, the plane which dropped the atomic bomb, the day after the bombing. As the Americans were nice enough to give them the picture, the Japanese were so thankful that they ended their war with America the next day. The Japanese wanted vengeance over the bombing and thus killed every dolphin and whale they see. Stan almosts blurts out the fact that it was indeed the Americans who bombed Hiroshima and not dolphins and whales but Cartman whispers that if the Japanese do find out the Americans caused the bombing, they will wipe out and kill every American they see. Stan then proceeds to call Kyle to photoshop the picture to a chicken and a cow flying the Enola Gay.