The Atomic dome in Hiroshima. The bomb exploded c.600m above the city and killed everyone inside this building. Very poignant and kept as a reminder of the damage caused and victims killed.
There's also museum near by listing the 27,500 registered who died but there was an estimated 350k who died from their injuries caused by the blast.
This is probably more political and legal but put it here because it's not currently following the flow of discussion. Quite interesting the difference in legal burden and the price of low crime rates.