To recap, the Rahway Valley Railroad was a short set of tracks that shuttled between the modern-day Morris & Essex line and Raritan Valley line. It was formed in 1904 and closed in 1992 after a long decline.
When I explored a few weeks ago, I did not succeed in finding the tracks.
But this week, I took a roundabout route, all the way through the long Hidden Valley Park (which lies adjacent to the area of interest, and it is an official Union County Park and therefore legal for me to traverse. Look, they publish a PDF map and everything, it’s got to be okay).
Incidentally, now that I’ve traveled the path, if I were to do it again, I’d start behind the Knights of Columbus; there’s a sort of a trail head behind their parking lot, which is much closer to the tracks. I’d also bring a friend; I got a really creepy vibe from those woods. (No human remains [that I saw], don’t worry.)