The Naruto area is famous for two things, the whirlpools at the bridge, and the Otsuka Art Museum.
You can either take a boat ride to both view and feel the whirlpools, and the heavy current under the bridge. Alternatively, you walk under the bridge to get a closer look at it all. If you do the latter, make sure you go for one of the tours that allows you do walk outside under the bridge.
The Otsuka Art Museum is a bit of a strange museum, as it includes a collection of replicas of most of the famous arts in the world. So if you are not a fan of walking in every art museum, this would be the museum for a life time, all the art in one place. No need to visit any other place after this. They even have full size replica of some of the church paintings from Europe.