So I was doing some research on the Queensboro Bridge and came across this article about the old Queensborough Bridge Railway terminal. If you come off the Queensboro Bridge onto 2nd Avenue, you've probably seen the little station hut that still exists on the 2nd Avenue plaza. I've always wondered what that was (I just assumed it was a bathroom sort of like the Allen Street one) but it's not. It used to be a station entrance and if you look closely, there are remnants of the railway still in plain sight today.
The next time I ride across this bridge I'll try to get some proper photos. But you can see some here if you want to get a sense of what's still visible.