Otawara castle is south of Otawara on a hill overlooking the river and the town.  There is no castle anymore, but you can see where it was and also the original layout on a map below the site.  

Originally constructed in 1545 by Otawara Sukekiyo, Otawara Castle was the residence of Lord Otawara. Before battle of Sekigahara, 1600 Tokugawa Ieyasu ordered the repair of the Castle, but now all that remains are stone markers for the edge of the keep.  
It is planted with Cherry trees and Hydrangeas and is lovely in spring..

Information from: http://www.ohtawara.info/spot/ryujyou.html