Ako Castle was built in 1648 by order of Asano Naganao, incorporating the insights of military scholar Yamaga Soko as a "flat castle opening onto the sea." Its practical layout, including sharply angled stone walls and multi-directional gates, is a notable feature.

The castle ruins were designated a National Historic Site in 1971, and the feudal lord's gardens in the Ninomaru and Honmaru were designated National Places of Scenic Beauty in 2002. They continue to be maintained as cultural assets that convey the scenery of the past.

The large pond south of the Honmaru and the vast group of ponds in the Ninomaru are so large that records show that they were even used for boating. Currently, restoration and public access are underway based on excavation findings, and the area is a popular photo spot, showcasing the seasonal light and the changing colors of the water. Cherry blossoms, fresh greenery, and the colors of late autumn beautifully overlap the stone walls and moat, making for a relaxing stroll around the castle ruins park.

Free parking is available on the north side of the castle.

[Trivia]
- Ako Castle is a rare flatland castle with the characteristics of a "sea castle," accessible by boat through the Suitemon Gate on the Seto Inland Sea side.

[Hidden Gem]
In the castle's Sannomaru bailey is Onishi Shrine, dedicated to the Ako Roshi.