Tsuwano Castle, Mountain fortress in Tsuwano, Japan

Tsuwano Castle is a ruined mountain castle on Mount Reikizan, a 367-metre peak in the southwest of the Tsuwano Basin. Its summit, about 200 metres above the town, keeps stone walls, the tenshudai platform built with quartz diorite blocks of over two tonnes, and dry moats. The Sanjikkendai, the highest point, overlooks the castle town.

Yoshimi Yoriyuki was posted to western Iwami as jitō for coastal defence after the Mongol invasions, and in 1295 his family began building Sanbonmatsu Castle on the south side of Reikizan; it was completed in 1324 under his son Yorinao. The Yoshimi held it for fourteen generations. In 1554, during the siege known as the Battle of Sanbonmatsu Castle, the castle withstood more than 100 days against Sue Harukata's forces. The Yoshimi left for Hagi after the Western Army's defeat at Sekigahara in 1600, and Sakazaki Naomori rebuilt the summit with stone walls and a keep.

The castle's name changed with its owners: it was Sanbonmatsu (or Ipponmatsu) Castle under the Yoshimi, and the Sakazaki moved the main gate to the former rear approach. The Kamei clan, lords from 1617 to the Meiji Restoration, founded Taikodani Inari Shrine in 1773 on the ridge inside the castle grounds, and the Chugoku Nature Trail now links it with Washihara Hachimangu below.

From Tsuwano Station on the JR Yamaguchi Line it is about a 40-minute walk to the lower station of the castle ropeway; the ride up takes 5 minutes, and the summit enclosure is about 15 minutes on foot from the top station. A free car park for 30 cars sits by the ropeway entrance. The Chugoku Nature Trail also climbs through the castle grounds between Washihara Hachimangu and Taikodani Inari shrines.

The mountain top was levelled under the Sakazaki clan and fitted with stone walls and a three-tier keep; the keep platform's quartz diorite blocks weigh over two tonnes each. The keep stood in the second enclosure, not the main one, and burned down after a lightning strike in 1686, never to be rebuilt.