Sannohejo Castle is a mountain castle on the hill with an altitude of 130 metes in the middle of Sannohe Basin. The castle is fortified with two rivers of the Kumahara River and the Mabechi River that flow together to the north of the castle and the damp ground spreading to the south. On the hill were the province office building, the domain lord’s residence, storehouses, houses for samurai warriors, and the three-story watch tower. These buildings are said to have been completed in around 1591, when the 26th generation of Nanbu Province, Nobunao Nanbu ruled this region. The castle town also developed at the foot of the hill. In 1967, the three-story four-floored donjon in the early modern donjon style named Onko-kan was constructed, where historic documents including the ones about domain lords are displayed. Tsuna-gomon Gate was also reconstructed recently. The two of the castle gates now exist as the main gates of Hosenji Temple and Ryusenji Temple in Hachinohe Town. In the site of the castle ruin are Nukabe Shrine that enshrines Mitsuyuki Nanbu, the founder of Nanbu clan, garden, and other cultural facilities. A lot of people visit to enjoy walking or seeing cherry or plum blossoms and maple trees.