Odani Castle, Mountain castle in Nagahama, Japan

Odani Castle is a Sengoku-period mountain castle in Nagahama, Shiga Prefecture, built along the ridges and valleys of Mount Odani. Its main enclosure runs over 800 meters north to south, and with outlying fortifications the site exceeds one square kilometer. A dry moat about 20 meters wide divides the main area; behind it lie the older enclosures, while the palace compound in front was protected by stone-lined ramparts and a compound gate.

Construction of Odani Castle began around 1516 under Azai Sukemasa, and it was held by 1525 when the Rokkaku invaded. Oda Nobunaga's forces besieged it for four years during the Genki and Tenshō eras; the castle fell in 1573, and Azai Hisamasa and Nagamasa killed themselves. Hideyoshi later dismantled it for materials for Nagahama Castle.

The castle holds recognition as one of Japan's Five Greatest Mountain Castles, alongside Kasugayama, Nanao, Kannonji, and Gassantoda fortifications.

Access requires a 45-minute walk from Kawake Station followed by an hour-long mountain hike. The path crosses steep terrain with narrow trails, so sturdy footwear and enough water are recommended.

The castle's stone walls were advanced for their time: the Azai clan likely needed them to show local lords they had become true Sengoku daimyo rather than minor vassals. A 5 m high stone wall still stands east of Sanno Maru, and stone-lined gateways remain at several enclosures.