Don't forget to look out for the crossing of Hadrian's Wall. The first crossing at Greenhead - about four and a half miles West of Haltwhistle - is not actually visible, but it's just before the ruins of Thirlwall Castle, which you can see on the right from the train. However a mile or so further on, at Gilsland, the line re-crosses the wall and a well-preserved stretch of it can clearly be seen crossing the fields diagonally away from the railway in front of the big country house.
EDIT: Also on the right - about a mile before reaching Corbridge - you may catch a glimpse of the original Farnley Scar Tunnel dating from the opening of the line in 1834. In the later part of the 19th century, the North Eastern Railway deemed it too narrow and low for 'modern day' traffic and bypassed it with a cutting. At this time of year it may be difficult to spot because of encroaching vegetation and - IIRC - it's easier to see from the Corbridge end rather than the Riding Mill end. Wylam and Hexham have the last two remaining NER gantry-mounted signal boxes and Corbridge has the famous 'Valley' Indian restaurant in the station building. The whole line is packed with railway and scenic interest and - IMHO - very much underrated.
