Tatsuoka Castle
Saku, Japan · built 1867
Tatsuoka Castle (Tatsuoka-jō) was a Bakumatsu period pentagonal "star fort" located in what is now part of the city of Saku, Nagano prefecture. It was the primary fortress of Tatsuoka Domain, ruled by the Ogyū-Matsudaira clan. Along with the Goryōkaku in Hakodate, Hokkaidō, it is one of only two star fortresses in Japan, and the castle ruins have been designated as a National Historic Site since 1934.
Fort data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).