Sunpu Castle has several Japanese names including Sunpu-jō, Fuchū-jō and Shizuoka-jō. The most descriptive English version is Castle of the Floating Isle because, during the 17th century, the fortress was encircled by three moats. This style of concentric rings is called rinkaku. The design was exceptionally expensive so rare in Japan. Two of the deep defensive waterways remain. This is the innermost moat at North Gate. Half of this footbridge was reconstructed in stone. The original was wooden.