The Oya Museum (大谷資料館) is the site of the Oya Stone Mine (大谷採石場). The mine dates from at least the eighth century AD and stone from the mine was used widely in the area. Removal of stone from the mine has created cavernous a space with a floor area of about twenty thousand square metres underground. Today, many events and concerts are held in the mine.
Access
0. at Utsunomiya Station
1. use Kanto Bus to Shiryokaniriguchi (30 min.)
2. walk (3 min.)
600 JPY
1 hr.
Let's learn MJER Iaijutsu. 
映画好き集まれ！ 
Stone from the Oya Stone Mine was already popular in the year 741. The stone tower of the Kokubunji Temple was built using Oya Stone. In the year 810, the Oya Kannon statue was created on the side of a cliff using Oya Stone. In the Showa period (1926-1989), the mine produced over 800,000 tons of stone per year. There are more than thirty stone mines still is use in the Oya area, and the Oya Stone Mine is now for open as a park and venue for events.
official homepage: http://www.oya909.co.jp/