Hakusan Castle, Mountain fortress in Nirasaki, Japan.

Hakusan Castle is a yamashiro on a 573-meter ridge in Nirasaki, measuring about 150 meters east-west by 180 meters north-south. Its enclosures are cut by vertical dry moats, with two large moats on the ridge behind the west side. Signal towers stand at the tips of the north and south ridges.

The fortress was built during the Heian period as the primary stronghold under the warlord Takeda Nobuyoshi. Later it served Tokugawa Ieyasu as a strategic position against the Odawara Hōjō clan.

The name comes from the Hakusan Jinja, a Shinto shrine that occupied the mountain before the fortress was built. This spiritual connection between the sacred site and the later military structure remains visible to visitors exploring the ruins.

The ruins can be reached by a short walk from the Nabeyamagami bus stop, which connects to Nirasaki Station. Wear sturdy footwear since the path crosses uneven mountain terrain and conditions vary with the season.

The site survived two attempts to convert it into a quarry, preserving rare examples of intact fortress structures. Multiple levels of terraced enclosures and gate foundations demonstrate construction techniques lost at other locations.