Originally Posted by
RichardInSF
I took a private rail line that was single track. It included a stop where you could tour an old, no longer active, copper mine. At another stop, you could get off and go to a small rural onsen. Now I can't quite remember where it is and how to get there, can anyone help?
You'll find onsen in every corner of Japan, but copper mines and non-JR railways narrow things down a bit.
Ashio mine +
Watarase Keikoku Railway?
https://www.nippon.com/en/guide-to-japan/gu900201/
Kamaishi mine + Sanriku Rias line?
https://www.sennin-hisui.com/kozan/kengaku.html