The only prison in Naegi Castle was located on the far left of Ō-mon Gate that separated Ni-no-maru (outer citadel) and San-no-maru (outermost region of the castle). The size of the building was about 4 m x 8 m (approx.13 x 26ft). It was built on a huge rock in a location that didn't get much sunshine. During the political dispute arising in Naegi Domain around the beginning of the Meiji era (1868-1912), a number of high-ranking samurai worriers were imprisoned and sentenced.