The Sengan Yagura is an important corner turret of Osaka Castle, strategically positioned to defend the Otemon-gate. Its design allows for flanking attacks on enemies approaching the Ōte Gate, with its west and south sides facing the moat. The turret was originally constructed in 1620 (Genna 6) during the early phase of Osaka Castle's reconstruction under the Tokugawa Shogunate. The construction was overseen by Kobori Enshū, renowned as a tea master, and it is considered one of the oldest structures of Osaka Castle, along with the Inui Yagura, which was built at the same time. The name "Sengan Yagura" originates from a historical anecdote during Oda Nobunaga's siege of Ishiyama Hongan-ji. It is said that Nobunaga promised a reward of 1,000 kanmon (a large amount of currency) to anyone who could capture the turret. Since then, turrets bearing the same name have been established in successive castles, including Ishiyama Hongan-ji, Toyotomi Osaka Castle, and Tokugawa Osaka Castle. The turret's interior is equipped with gun ports and stone-dropping mechanisms designed to effectively repel enemy invasions. The structure itself is slightly tilted by approximately 1.8 degrees, giving visitors a unique sensation when inside. During the Meiji era, modifications were made by the former Imperial Japanese Army. However, in 1961, restoration work returned the turret to its original design from the time of its construction. Today, the Sengan Yagura is designated as an Important Cultural Property of Japan, highly valued for its historical significance.