[1] Nanao Castle is located on the top of Mount Shiroyama, a 120-meter hill overlooking the Hamada Plain at the estuary of the Takatsu and Masuda Rivers in western Shimane prefecture.

The castle is located on a strategic point controlling the junction of the ancient San'indō highway and the Kitaura Kaigō (leading towards Hagi) and Masuda port on the Sea of Japan.

This castle was arranged in a "Y"-shape on the top of Mount Shiroyama and was protected by combination of sheer clay walls and narrow paths.

The Masuda held out at Nanao Castle for half a year, but eventually were forced to capitulate, losing much of their territory, and to accept the Mōri as their overlords.

During archaeological excavations, more than 40 large and small enclosures, dry moats, earthen walls, and the remains of wells were unearthed, along with the foundations of many buildings from the late Sengoku period.

The castle site, now occupied by a small Shinto shrine, is a 20-minute walk from Masuda Station on the JR West San'in Main Line.