The original Iwakuni-jō was built by Hiroie, the first of the Kikkawa lords, between 1603 and 1608. Just seven years later, the Tokugawa shogunate passed a law limiting the number of castles daimyō were allowed to build, and the castle at Iwakuni was demolished. It was rebuilt not far from its original setting in 1960. Inside there is a small museum of samurai swords and armour, and good views from the hilltop setting.
You can get to the castle by cable car (one-way/return ¥320/550; combination return ticket including castle and bridge ¥940; every 20 minutes), or walk up among greenery and bird life on a pathway from the west side of the park. The steep walk takes about 45 minutes.