If bits of bridges and things Just up near top of Nursery lane at Sprotbrough, Just had a look its still shown on Google maps as old bridge over road, Used to be able to walk almost to Conisbrough along old cutting, Didn't think it would still be there last time I was over there was 38 years ago! Also near to Denaby ings nature reserve, If you go from Mexbrough you need the embankment on the left hand side, Right hand side is the nature reserve It is popular with walkers though, And the reserve car park is said to be popular with wife swapping people at night!
Personally, I'd go to Elsecar. Between Rotherham and Barnsley.
They have a few miles of track, which is used to run old steam locomotives up and down for tourists. They don't really go anywhere. Just to the end of the track and back. This is mostly at weekends/bank holidays, etc. Which means the track is disused during most of the week.
Of course you might want to confirm there's nothing running on the day you shoot.
Elsecar also has a heritage centre plus all the old trains, and an old fashion station; all of which means you can get a variety of shots, while you are there.