Château de Tsukui, Mountain fortress in Sagamihara, Japan

Tsukui Castle is a mountain castle (yamajiro) on Mount Shiroyama, 375 m high, in Midori Ward, Sagamihara. It is a typical early example of a negoya-style castle, with two negoya (base settlements) to the north and south. Excavations have found post-hole buildings, dry moats, earthen ramparts and a gunpowder store at the O-yashiki site.

The fortress emerged during Japan's Warring States period as an important outpost and was abandoned during the early Edo period. The shift from warfare to peace made this mountain stronghold unnecessary.

The name Tsukui predates the reservoir: Lake Tsukui is a dam lake created in the Showa era, after the castle was gone. The castle is also written 筑井城, linked to the Miura clan's Chikui family, said to have built it in the Kamakura period. The neighbouring former town of Shiroyama took its name from the hill's eastern foot.

The main castle area lies in Negoya, Midori Ward, Sagamihara, and is now part of Kanagawa Prefectural Tsukuiko Shiroyama Park, with hiking courses laid out across the site. The summit of Shiroyama stands 375 m high, so the climb is uphill and the ground is uneven in places; wear sturdy walking shoes. Note that Tsukuiko lake beside the hill is a dam reservoir created in the Showa era, after the castle was gone.

The grounds have been transformed into Tsukuiko Shiroyama Park, where historical remains sit alongside hiking trails and recreational areas. This blend allows visitors to experience both fortress history and nature in a single visit.