Oya Peace Kannon & Oya History Museum (Nakajima Aircraft Underground Factory Ruins)

The Oya Peace Kannon (大谷平和観音) and the adjacent Oya History Museum (大谷資料館) are located in the Oya district approximately 8 kilometers northwest of central Utsunomiya. Together they constitute one of the most significant war-related heritage sites in Tochigi Prefecture, combining a monumental peace memorial with the physical remains of a secret wartime underground aircraft factory.

Oya Peace Kannon:

The 26.93-meter (88 shaku 8 sun 8 bu) Kannon statue was carved directly into the exposed Oya stone cliff face over six years, from 1948 to 1954, with the formal dedication ceremony held on May 4, 1956. The statue was conceived by Ueno Namizo, a Gunma Prefecture native who had been mobilized to work in the Oya underground factory during the war. After the war, driven by the desire to memorialize two younger brothers lost during the war and all who perished in the conflict, he devoted himself to Buddhist sculpture and initiated the carving of this massive relief, which was executed under the direction of the sculptor Tobita Asajirō, a professor at Tokyo University of the Arts. The statue's circumference spans 20 meters, and it has become the most recognizable landmark of the Oya district. It is registered by the Ministry of Internal Affairs and Communications as an official civilian war-dead memorial facility.

Nakajima Aircraft Underground Factory:

As Allied bombing devastated Nakajima Aircraft's main factories (particularly the Musashi Works in Musashino, Tokyo), production was urgently dispersed to numerous satellite locations. The vast underground caverns of the Oya stone quarries — formed over decades of mining the distinctive light green tuff — were commandeered as an ideal bomb-proof factory. Two main production lines operated underground: the Utsunomiya Works (producing airframes) and the relocated Musashi Works (producing engines), both manufacturing components for the Ki-84 "Hayate" (疾風, Allied codename "Frank"), widely regarded as the finest Japanese fighter aircraft to achieve mass production during the war.

A large workforce was mobilized for underground production, including regular factory employees, conscripted laborers, and mobilized students. The underground space, covering over 20,000 square meters (approximately 140m × 150m), maintained a constant cool temperature — the same characteristic that today makes it a popular tourist attraction and event venue.

Oya History Museum:

The museum, opened in 1979 within the former quarry, allows visitors to explore the cavernous underground halls that once echoed with aircraft manufacturing. The space is now used for art exhibitions, concerts, film shoots, and weddings. The underground caverns maintain an average temperature of approximately 8°C year-round. The museum preserves the physical evidence of both the centuries-long Oya stone mining tradition and the wartime industrial mobilization.