The Barrow Hill Rail Ale Festival on the 21st of May, can you just show up, pay at the gate of go round the place taking photos of the locos around Barrow Hill? i have no intrest for the beer or ale
Apart from the main roundhouse, you can not get near most of the locos, your best bet is to go up there any Saturday or Sunday, (I think its open 10-4) and all you pay is a contribution of your choosing, rather than the beer festival price.
Obviously a lot more of the site is open then, as during a beer festival they won't want drunks in all the cabs pretending to be a train driver!
I have been a couple of times, and being a train and real ale fan its right up my street, but if you click on my photo gallery link in my signature below, there is a couple of galleries which will give you an idea of what you can see during the beer festival.