From the Exploration Unit
You've probably seen this place in different movies, or may have seen the locations it's inspired in manga and video games. The first images I saw of it where from 2012's James Bond film Skyfall.
It was a coal mine for decades, and over the years buildings were added to support the workforce there, peaking at over 5000 inhabitants in 1959. For a couple of grim decades it was a slave labor camp as Japan forced Chinese and Korean war prisoners to work the mines.
Eventually petroleum replaced coal in the 1960s in Japan and the mine shut down.
Now it's a tourist destination, and a reference for a future location in my comics.
You can read the history of it here: LINK
-Jake