Kamiizumi Castle (上泉城, Kamiizumi-jō) was a Japanese castle located in the province of Kōzuke (present-day Gunma Prefecture) during the early Sengoku period of Japanese history.^[1] Although the castle is destroyed, it is best known as the birthplace of Kamiizumi Nobutsuna.^[2] It is known that Nobutsuna's father made sure that his son was well-versed in the ways of bujutsu (martial arts) and he thoroughly trained his son many times near his castle. Through his father's training, Nobutsuna soon became a master of the spear and sword.