I had always wondered as a kid why such seemingly unimportant (to me at least) cities such as Hiroshima and Nagasaki were chosen as the A-bomb targets. The Peace Museum does a wonderful job of setting the scene for this (Hiroshima was always an important military port and there were thought to be no American POWs in the area), mixing in the history with copies of correspondences between those central to the formation of the bomb and planning of the drop, dioramas depicting the city before and after, explanations of the science behind nuclear armaments and, most poignantly, the personal stories and effects of the victims, many of them children.
I definitely recommend that anyone going to Japan visit Hiroshima - and not just for the Peace Park. While I might not have posted pictures of it (too busy enjoying) the modern city (and reconstructed old castle) was worth checking out. As, I'm sure, is the Mazda Museum with it's 7km long assembly line - sadly, I was in Horoshima over the weekend and, so, it was closed!