Imai Castle

Imai Castle is a fortified site positioned on a river terrace approximately 100 meters above the Shinano-gawa river in Tsunan. The ruins display concentric ditches and clay ramparts built into the elevated terrain.

The site was built in the mid-16th century as a watchtower for the border between Shinano and Echigo provinces during feudal conflicts. It served strategic purposes during struggles between major regional warlords.

The castle demonstrates how medieval Japanese commanders adapted fortifications to the land around them. Visitors can observe how natural features were incorporated into defensive planning.

The site is accessible by car, roughly 45 minutes from the Kanetsu-do Expressway at the Ishizawa-Shiouti interchange, then via Route 117. Walking trails cross the grounds, though the terrain is steep and uneven in places.

The fortress sits on a terraced peninsula with steep cliffs rising on three sides, creating a natural defensive barrier. This geographic arrangement meant attackers had very limited options for approaching the position.