Oka Castle was originally built in 1185, then later torn down during the Meiji Restoration along with many other castles in Japan. However the stone wall foundation still exists and along with the sprawling castle grounds, it is one of the main tourist sites in Taketa.

Found on top of a hill, the ruins offer a stunning panoramic view of the surrounding mountains.  The castle is also the perfect location to hear Taki Rentaro's famous melody, "Moon Over the Ruined Castle;" through some feat of engineering which is a mystery (to this author), Taketa City has constructed some kind of structure which plays the melody as cars zip down Route 502 (seriously -- walk up to the shrine and pay attention as cars come down the road).

The ruins are the most popular in spring and autumn for their stunning sakura blossoms and autumn foliage display, respectively. 

There is a small fee to enter the castle grounds.