Iwamura Castle was located in the southeastern area of Mino Province in Japan. Its ruins can be found in the modern-day municipal subdivision of Iwamura, in Ena, Gifu Prefecture. Along with Takatori Castle in Nara and Bitchu-Matsuyama Castle in Okayama, it is regarded as one of the three best mountain castles, and at an elevation of 721 meters above sea level, it is one of the highest in Japan.

Lady Otsuya was a Japanese female samurai (onna-musha) from the Sengoku period. She was the ruler of Iwamura Castle until the last days of her life.