This turret is situated at the northwest corner of Nishi-no-maru Garden and is one of the oldest structures in Osaka Castle. The Inui Turret, as well as Sengan Turret, was designed and constructed by Enshu Kobori. It is two-storied and has an unusual L-shaped structure. The first and second floors are exactly the same in size and style. The turret with a watchtower on it is said to have been from the original Main Tower. This Turret is an example of an older building style. When the turret was disassembled for restoration, a roof tile bearing a note written with a spatula was found and it was thus verified that this turret was constructed in 1620.