Fukurō no Shiro (梟の城, Owls' Castle) is the ninja-themed 1959 debut novel of Japanese author Ryōtarō Shiba, which won him the Naoki Prize in 1960 after the story was published by Kodansha. It has been adapted into a 3-part "Naoki Award Series" TV broadcast on the Fuji Television Network in 1960, and into two jidaigeki-genre films, Castle of Owls in 1963 and Owls' Castle in 1999.