Yokoku Castle was built in 1602 by the first leader of the Hiji Clan, Kinoshita Nobutoshi, with the assistance of Hosokawa Tadaoki.

The castle was originally called Hiji Castle, Aoyagi Castle or Ukitsu Castle. The third clan leader, Kinoshita Toshinaga, took an excerpt from an old Chinese book called 'Enanji', which stated that: 'The sun rises from Yokoku and shines on Kanchi', and changed the name to Yokoku Castle.

Today, the castle site is used as the Hiji Elementary School, but certain parts of the castle, such as the Kimon tower and the back gate, are being reconstructed.

A park has been established around the castle base, and is a popular spot to take in and appreciate the entire view of Beppu Bay. The seashore at the foot of the castle ruins is called Shiro-shita-karei, and is famous for deriving its name from the Shiro-shita seashore. There is also a spring, which is one source of fresh water for this region.

The remains of Fukuoka Castle are located in Chuo-ku, Fukuoka. The castle was originally constructed in 1601 by the founder of the Fukuoka clan, Nagamasa Kuroda. It took seven years to complete and also goes by the name of Maizuru-jo, or Dancing-Crane Castle.

It is a castle positioned on the flat top of a hill, and once had at least 47 different watchtowers and turrets of different sizes. Because it did not have a significant tower keep, it was never looked upon as a threat by the central government, which explains why it stood without damage through the Meiji period.

The castle features several three-storied turrets known as yagura: Tabun Yagura (an Important Cultural Treasure), Shiomi Yagura and Kinen Yagura, as well as the Moritaheitei Nagayamon Gate and the Najima Mon Gate. The Dai Tenshudai has become an observation deck. In the area surrounded by the castle moat, can be found Cyperus Ohwii trees, designated by the prefecture as a protected species. There is also a monument commemorating the 'Manyoushu' poetry classic.

At present, the surroundings of the castle have become Maizuru Park, and there are also several sports facilities, such as the Heiwadai Track and Field Stadium. The castle is also a famous cherry-blossom viewing spot. In Showa 32, the castle was designated as a national historic site.