Fukakusa Castle was built during Japan’s Middle Ages. It is said to have been a residential castle paired with Yato-jo Castle, or the residential castle of Hemi Mitsunaga, the eldest son of Hemi Kiyomitsu. In Kai Kokushi (Official Records of Kai Province), it is written that the castle was the residence of a figure called Horiuchi Shimousanokami at the end of the Warring States Period (1467–1615), but it fell into decline after his son Chikaranosuke took over.
The castle site spreads roughly 50 meters east to west and 130 meters north to south. On three sides, it is separated from the surrounding land by an artificial moat, and on the remaining west side, Nishikoromo River provides a natural moat. The inside perimeter of the moat is defined by an earthen embankment 1 to 2 meters high. Additionally, there are enclosures on the south and north sides of the site. The south enclosure used to be divided by another earthen embankment.
An excavation of the land outside the site on the northeastern side yielded a discovery of building ruins and artifacts dating from between the 15th and 17th centuries. The ruins have been preserved well, and the site is an important historical site for medieval history studies.