The Ōya History Museum in Utsunomiya, Tochigi prefecture is the site of the famed Oya stone quarry. The quarry has reached its gaping size being dug out over the course of 70 years. This fantastically huge underground space is almost like a different world. It was used as a secret factory during wartime and has recently been gaining popularity as an event space, even wedding ceremonies have been held here. It can be seen appearing in all kinds of movies, dramas and TV commercials.

This "land of the unknown" is 20,000 meters squared and 30 meters deep. The dimly lit sprawl of rock face makes you feel like you are lost in an actual fantasy dungeon. It's guaranteed Instagram gold with many people already reaching out on social media in hopes someone will find them down there. As it is underground, there is a lot of mist, and with an average temperature of around 8°C, it can get chilly, so don't forget to bring your coat. Of course you could always rely on their complimentary blanket rental service.