Also known as Carp Castle (Rijō; 鯉城), Hiroshima-jō was originally constructed in 1589, but much of it was dismantled following the Meiji Restoration. What remained was totally destroyed by the bomb and rebuilt in 1958. In the north end there's a small five-level museum with historical items, but most visitors go for the tower with views over the impressive moat. The surrounding park is a pleasant (and free) place for a stroll. Enter from the east or south.
There are samurai performances at the south entrance every Sunday at 1.30pm and 3pm; and parades every Saturday at 1pm and 3pm.