I've seen a reasonable amount of the bits of the rail network not witnessed by many regular passenger trains over the last couple of years, primarily courtesy of Crosscountry services.
I've done the Stllington line from Ferryhill to Stockton (Freight only normally) while en route to York.
I've been on a Voyager routed direct from York to Sheffield via Sherburn-in-Elmet and Pontefract Baghill. It took me months to fathom out what had gone on there: I recall passing a depot filled to the brim with withdrawn 56s (Turned out to be Ferrybridge) and remember seeing the "Pontefract" station signs as we passed through.
I've been round the "old road" from Sheffield to Chesterfield via Beighton and Barrow Hill a couple of times: Once on a railtour, and once on an XC service that was bypassing an EMT service that had failed around Dronfield.
I've also been on one of the XC services that was diverted from Wichnor Junction to Lichfield on the freight only line through Alrewas, and then down the Cross-city line into Birmingham.
Finally, I boarded a southbound Wrexham & Shropshire service at Tame Bridge Parkway that traversed the Hamstead chord between Perry Barr and Soho Junctions. Nothing too unusual about that, as that is the route taken by LMs' Chase Line services, but there was a difference: It was a mid-winters day and was snowing heavily, and the train was already running over an hour late by the time it reached Tame Bridge Parkway (It had been touch and go for a while as to whether it would run via Tame Bridge at all, or whether it would take the more direct route via Sandwell & Dudley and bypass us altogether to make up time). Shortly after we had boarded it was announced that there was a non-functioning windscreen wiper and the train would have to be turned at the earliest opportunity so that the "good" cab was leading. This was effected by bringing the train to a halt beyond Perry Barr South Junction, and then reversing our direction to run over the usually freight only chord between the South and West junctions onto the Hamstead Chord to continue our journey.