This abandoned railway follows a natural riverbed, which are hart to come by in Japan. I heard about it on the internet and went over to see it. Despite it being abandoned and half a dozen signs stating "This is NOT a hiking trail!" there were lots of people out there with their kids. Because it's a railroad, it's flat and has a nice view. A pretty perfect walking trail.
The best parts were the tunnels. There were about 6 or 7 of them and walking a mere ten steps inside rendered you in complete and utter darkness. Without a flashlight, they'd be impossible to walk through. The temperature also dropped about 10 degrees in that darkness. Shining my flashlight around I found writing on the walls, hooks set into the walls, and sometimes little alcoves that must have served some purpose in the past.