This is a VERY interesting and beautiful place.
What brought me there was my interesting in the Naruto anime, so I wanted to go to the Naruto bridge to see the "Uzumaki" or "Whirlpools". it's a bit far and expensive to go from Osaka, but I found my time well spent.
It's something I'd never seen before and it was beautiful, but I expected more, deeper whirlpools... I found out we have to go in the right season and at the right times.
Next time, I should arrive early and take the boar to go straight inside the whirlpools, that seemed very cool and not so expensive.
Also, I went to the bridge museum nearby but it wasn't so interesting... But since there aren't many things to do nearby, I think it was worth it going as well.
In this place, if you are going from Osaka, you will probably spend all day (to be able to see the high tide and arrive early enough to buy the boat tickets) and won't be able to see much more than the museum and the whirlpools.
But its a cool and unique place I would go again with my wife if I had a lot of time in Osaka.