Château d'Hanazawa, Mountain fortress in Yaizu, Japan.

Château d'Hanazawa is a mountain castle on a 150-metre hill in Takasaki, Yaizu, reached by a ridge extending southeast from Mount Takakusa. Its summit holds a 29-by-65-metre main enclosure and a 28-by-66-metre second enclosure, with waist enclosures and dry moats cut along the surrounding ridges across a 450-metre north-south span.

Hanazawa Castle was built as a mountain stronghold guarding the western approach of the Imagawa, the shugo of Suruga. The Suruga Shiryō dates construction to 1492–1503, but scholars place it around 1537, after the Hanakura no Ran, with Sekiguchi Ujikane as first castellan. In 1570 Takeda Shingen attacked; Ōhara Sukeyoshi held out for 14 days before surrendering and withdrawing to Tōtōmi.

The castle's name is written with the characters for "flower" and "marsh". The first lord was Sekiguchi Ujikane, a retainer of the Imagawa, and in 1570 Ōhara Sukeyoshi (also called Obara Shigemitsu) held the castle for fourteen days before surrendering to Takeda Shingen's army and withdrawing to Tōtōmi. Since 2018 the city of Yaizu has run a project to open the site, laying walking paths and clearing trees so visitors can see the earthworks.

From Yaizu Station's south exit, take the Yaizu Loop Line bus to the Takakusayama Ishiwaki stop. The castle grounds lie a short walk uphill from this point.

Excavations in 2018 uncovered foundations and wall remnants that reveal the construction methods and defensive thinking of the original builders. These findings offer rare insight into how medieval Japanese engineers adapted their designs to the mountainous terrain.