Najima Castle, Japanese castle ruins in Higashi-ku, Japan

Najima Castle was a fortification built on a hill jutting into Hakata Bay with two enclosed areas, one to the north and one to the south. Today the site has been transformed into a shrine and public park with markers showing where the original structures once stood.

Tachibana Akitoshi built the castle as an outpost of Tachibana-yama Castle. In 1587 Toyotomi Hideyoshi granted Chikuzen to Kobayakawa Takakage, who rebuilt Najima as his residence and naval base. After the 1600 Battle of Sekigahara, Kuroda Nagamasa received the province, abandoned Najima, and used its stones and timbers for Fukuoka Castle around 1601.

The castle's gate was moved to Sōjō-ji in Munakata, and its rear gate now serves as that temple's gate; the Karamon of Sōfuku-ji, the Kuroda family temple, also preserves relocated parts. Sliding-door paintings from Najima Castle are held at the Kyoto National Museum. The name Najima-jō is used for the ruins and the adjacent Najima Shrine.

The park opened in April 2012 on land bought by Fukuoka City next to Najima Shrine, and you enter through the shrine grounds. Opening hours are 9:00–19:00 from April to September and 9:00–17:00 from October to March; admission is free. The former car park is gone, so come by public transport: Nishitetsu buses from Tenjin stop at Najima Undo-koen-mae in about 15 minutes.

The fortress was designed so that large warships could dock directly at its base, making it function as an unusual military harbor. This naval feature allowed ships and troops to be moved and supplied quickly when needed.