Naegi Castle, Mountain castle ruins in Nakatsugawa, Japan

Naegi Castle is a fortress ruin on Mount Takamori near Nakatsugawa in Gifu Prefecture. The site rises 432 meters above sea level overlooking the Kiso River and incorporates massive natural boulders into its walls.

The castle was built around 1532 by Tōyama Masakane on Mount Takamori, on the site of a fortification raised in the 1330s. It passed between the Takeda, Oda and Mori before Tōyama Tomomasa retook it in 1600 on Tokugawa Ieyasu's orders and was confirmed in the Naegi domain, which lasted until the abolition of the han in 1871.

The fortress takes its name from the town of Naegi and served as the power center for local lords over three centuries. Visitors can still observe how natural rock formations were integrated into defensive structures, connecting the site with the river landscape below.

The climb from the nearest stop takes about 30 minutes on a mountain path that becomes steep in sections. Direct bus connections from Nakatsugawa Station run in spring and autumn when weather conditions are favorable.

The gate doors and posts of the Ōte-mon survive and are kept at the Naegi Tōyama Historical Museum in Nakatsugawa, not at the ruins themselves. The castle also bore the name Akakabe-jō, "Red Wall Castle", because its walls showed bare red earth instead of white plaster; the domain could not afford the plaster.