Matsumoto Castle in Nagano Prefecture is one of the most attractive in Japan. It’s one of the few castles in Japan that is not a reconstruction and can be combined with a trip to the wonderfully historic Nakasendo.
Official castle website: http://welcome.city.matsumoto.nagano.jp/contents03+index.id+3.htm
Some interesting history and background: http://www.yamasa.org/japan/english/destinations/nagano/matsumotojou.html
I went to this same place a few weeks back actually- took almost the same photo of the castle as you! We visited on the way back from hiking and camping in Kamikochi, in the mountains. Cold.