Japanese castles I've visited: #3 Ako Castle in Hyogo Prefecture. I've been there a few times, mostly in autumn. There's no main tower left and nothing to enter, but a few nice turrets and moat as well as castle walls.
Japanese castles I've visited: #2 Akashi Castle in Hyogo Prefecture - which I've visited a few times. There's no main tower left, only turrets. It's located in a huge park right next to the train station.