is a city located on the northern border of Ōita Prefecture, Japan, next to Fukuoka Prefecture.
As of 2008, the city has an estimated population of 84,179 and the density of 171 persons per km². The total area is 491.09 km².
The city was founded on April 20, 1929.
Nakatsu is a castle town, and the castle can be visited. The modernised interior comprises a museum with samurai armour, old maps and information about Rangaku (Dutch studies), for which Nakatsu was an important centre in the Edo era. There are fine views from the top of the castle keep.
Visitors should also not miss the residence of the most celebrated member of the Okudaira Clan of Nakatsu — Fukuzawa Yukichi — and the memorial hall there. It is close to the castle and 15 minutes walk from the station. Entrance 400 yen.
Nakatsu's Mt. Hachimen is also home to the popular music festival, Concert on the Rock. This annual charity event sees over 30 international acts performing over a June weekend for the pleasure of Japan's music lovers. The natural surroundings make it one of the most picturesque rock festivals in the world.
Nakatsu City is located in the northwest corner of Oita prefecture, Kyushu. To the east of Nakatsu is Usa City, and to the southwest is Hita City. Nakatsu touches the border of Fukuoka-ken on its west. To the Northeast is Suohnada Sea. The city is 491.09 square kilometers. 80% of the city area is mountainous. There is a wide stretch of flat, agricultural land which begins at the mouth of Yamakuni River and extends to Mt. Ehiko.
Zyosui Kuroda built the original Castle in Nakatsu.