During the Warring States period in the Middle Ages, the Murakami Suigun was one of the maritime clans that dominated the Inland Sea. These clans were regarded as pirates by land-based clans. One branch of the Murakami was based on Innoshima, where they had a rudimentary wooden fortress. In 1983, a today’s concrete castle was built as a museum to house historic artefacts. It isn’t an authentic recreation. 

The main building has an interesting collection of arms and armour, and you can enter one of the watchtowers free of charge.  

Below the castle is Konren-ji Temple, sacred to the Murakami clan, where the graves of the clan members can still be seen.