The availability of locations to explore are obviously dependant on industrial history, geographic location etc, and based on this, it’ll change what can be potentially found and explored.
If he’s keen on research, and bearing in mind UE is very dependent on research, I’d start with looking at historical maps to see how your town has changed over the years.
Track the flow of rivers, streams, brooks. Look at old mills, hospitals, industrial sites on older OS maps and cross-check against what's there now. See if your local council has a historical archived photo site.
The hobby needs a great deal of legwork to get something out of it, so the link below is a good start. It's gotten a lot of us into scrapes and pains looking for things, but i'm happy with my little local hoard of knowlage. Good luck.