Kanayama Castle, Hill castle in Ota, Japan

Kanayama Castle is a ruined yamashiro on Mount Kanayama, a 235.8-meter hill in central Ōta. Its main enclosure, now the site of Nitta Shrine, sits at the summit, with stone wall remnants on the slope behind. The grounds include the Ninomaru and Sannomaru enclosures and the Sun and Moon ponds to the west.

The Iwamatsu clan built Kanayama Castle in 1469, and in 1528 retainer Yokose Narishige seized it, his family later taking the name Yura. In 1584, with the Yura lords held at Odawara, their mother Akai Teruko defended the castle for over 15 months with 3,000 soldiers. Maeda Toshiie took it in 1590 during the Odawara campaign, after which it was abandoned.

The castle grounds hold the Nitta Shrine at the site of the main enclosure, and a bust of Nakajima Chikuhei, founder of Nakajima Aircraft, stands in the southern enclosure. The hill was a shogunal forest from 1688, and matsutake mushrooms from Mount Kanayama were presented to the Edo shogunate every year from 1629 until 1867.

The ruins sit on Mount Kanayama north of central Ota; from Ota Station's north exit the guidance facility is about 2.8 km, roughly 50 minutes on foot or 7 minutes by taxi. The site is a park with trails linking the enclosures, and the guidance facility opened in 2009. No buildings are reconstructed, so expect earthworks, stone walls and ponds rather than gates or towers.

Excavations from 1992 found that the main gate's eastern earthen rampart wall was rebuilt five times. Its base stones were set 10 to 20 cm forward, a technique called ago-dome ishi, to stop the wall from sinking and tipping. This stonework contradicted the long-held view that Sengoku-period castles in Kanto had no full-scale stone walls.