In short
The Genbaku Dome is the only building left as it stood after 6 August 1945. It is a World Heritage site and borders the Peace Memorial Park and its museum.
Miyajima, forty minutes away, holds the torii of Itsukushima shrine, standing in the water at high tide. The whole island is listed.
What it really costs
Hiroshima costs less than Tokyo, Kyoto or Osaka, for a city well served by the Shinkansen. It is an economical base for western Japan.
Hiroshima okonomiyaki, layered and cooked with noodles, is the local dish and one of the cheapest meals in the country.
What nobody tells you
The Peace Memorial Museum is gruelling, particularly for children. It is visited late in the morning, not just before a journey, and many people come out with no appetite for anything else.
The Miyajima torii only stands in water at high tide. At low tide you walk out to it. Tide tables are public and decide when to go.
Miyajima's deer roam free as in Nara, but they are not fed: the island forbids it to keep them wild.