The Oya History Museum (大谷資料館, Ōya Shiryōkan) is a museum built inside a massive former stone quarry in northwestern Utsunomiya. The man-made caverns were originally developed during the Edo Period to mine Oya Stone, a soft, yet durable volcanic stone that is only found locally. Oya stone has been used over the centuries as a building and paving material, and has been utilized in famous structures such as the facade of the former Imperial Hotel in Tokyo.
Evidence of mining can be seen all around the area, with huge slices taken out of the hillsides and giant voids carved into the mountains. The underground mines remained in operation until 1986, and by then an enormous series of caverns had been carved into the ground. A building sits at the entrance to the mines and houses a small museum that explains the history and geology of the area and exhibits different mining tools used to excavate the rock over the centuries.
From there, visitors can descend into the museum's extensive underground halls which cover over 20,000 square meters and are more voluminous than Tokyo Dome. A large section of the excavations are open to explore, and you may want to bring a jacket as the man-made caves act as a natural air conditioner with an average year round temperature of around ten degrees Celsius.
Many of the halls are lit up with colorful lights and house art installations, while others have been outfitted to serve special purposes, including a room with a chapel and one with a stage cut directly out of the rock. The surreal mines are frequently used as event space. They have also served as venues for concerts, weddings, art exhibitions and shooting location for various commercials and music videos. A gallery exhibits photographs from many of these events.
From JR Utsunomiya Station (West Exit), take bus number 45 bound for Tateiwa (立岩) and get off at the Shiryokan Iriguchi bus stop (資料館入口, 30 minutes, 460 yen one way, 1-3 buses/hour). The museum is a five minute walk from the bus stop. The bus also stops in front of Tobu Utsunomiya Station along the way (20 minutes, 460 yen one way).
A 1-day combination ticket (大谷観光一日乗車券, Ōya Kankō Ichinichi Jōshaken), which covers the bus round trip between Utsunomiya Station and the Oya History Museum as well as admission to the museum and the Oya Temple, is available for a discounted 1850 yen at the tourist information office or Kanto Bus ticket office outside JR Utsunomiya Station or at the Utsunomiya Tobu Hotel Grande near Tobu Utsunomiya Station.