The Obikuruwa Yagura of Himeji Castle is a double two-story turret located in an area called Ido Kuruwa, estimated to have been built during the Keicho era, and is designated as a National Important Cultural Property. This turret is characterized by its semi-underground structure with no walls or doors on the inner side of the castle and covered by stone walls on the outer side, and has two upper and lower levels of openings for shooting, called “sama” (narrow space). The well-curved area where the obi-kaku turret is located was named after the well it once contained, but is generally known as “harakirimaru”. This name comes from an episode that took place when Himeji Castle was sold to Himeji City in 1912 and opened to the public, and is not the actual place where the seppuku took place. In addition, the walls of the well-circle are provided with an antechamber wall, which is noted as a unique structure among the earthen walls of Himeji Castle. These features make the obi-kurinagura and its surrounding area an important place for understanding the defensive structure and history of Himeji Castle.