A routine archaeological survey in the heart of central Seoul has uncovered train tracks that nobody seems to have known were still down there. Seoul retired its streetcar system in 1968, though I don't know (and I doubt) if this line was operational until the end.
Here's a view of the site from farther back.
There are going to be public tours of the site next week where the tracks will be uncovered. I didn't come close to making the cut, so I'm probably going to jump the fence again late at night.