Oita City is the most populous city in Oita Prefecture and is also the prefectural capital. It once flourished as a castle town, and during the Sengoku period, it was an important site for Christian missionary work. Nanban culture also developed there. Eventually, the city entered a period of rapid economic growth, which led to its successful development as an industrial city. Today, manufacturing remains a thriving industry, with many factories and businesses located within the city. The city is also home to many historical sites, such as the Otomo clan ruins and the remains of Bungo Kokubunji Temple. Other popular tourist attractions include Takasakiyama Natural Zoo and the Oita Marine Palace Aquarium "Umitamago."