Japanese castles I've visited: #6 Azuchi Castle Ruins in Shiga Prefecture. Only ruins are left, but some of the most extensive ruins I've seen. If you're in Shiga or a fan of Oda Nobunaga, then it's worth a visit!
Japanese castles I've visited: #61 Mihara Castle Ruins in Hiroshima Prefecture. Ok, this wasn't a very interesting castle. Very few ruins are left, but they are right behind JR Mihara Station. I went there when it was already dark.
Japanese castles I've visited: #34 Itami Castle in Hyogo Prefecture (but very close to Osaka). Only very few ruins left. Right next to JR Itami Station. I'd say it's only worth a visit if you're nearby anyways.
Japanese castles I've visited: #30 Hizen Nagoya Castle in Karatsu (Saga Prefecture). I was extremely unlucky with the weather that day and thus I also was the only one up there. Typhoon-like rainstorms although it was the end of December. Freezing cold!