Does the national rail website not like Grand Central ?
National Rail Enquiries doesn't sell tickets but it should offer the fastest journeys at the time you search for; it will redirect you to a train company site to buy the tickets.
I was trying to book LNER 1 way and GC the other but I just cannot figure out how to do it. It seems the GC may need 4 stops but when I try to select it my outward journey gets dumped off my selection.
It was all a bit easier 25 years ago when the grumpy guy behind the window had to look it up in a book !!!!
You can force this with Trainsplit by using the 'advanced options' and selecting different options for outward & return, you can force any particular TOC e.g. Grand Central.
Trainsplit also has a seat selector which even works with GC.
You would normally be issued with e-tickets which are super easy to use (you can print them if you want, but you don't have to: you can show them on any device, whether that be a phone or tablet computer etc).
Oh and advanced tickets, how close to day of travel can I book ?
Depends on many factors; for a weekday with LNER (excluding late evening) it can be many weeks ahead. But for a weekend with some train companies it could be literally just a few days!
Split my fare is a usable site at least.
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Just seen this; Splitmyfare is a branded version of Trainsplit. I've not checked if it offers a seat selector or not, but the fares it offers should be the same.
I will make sure to visit both York buildings, I plan for a whole day there and no one else with me, so if I want to geek out I will.
You may want to visit the York Tap (perhaps while awaiting your train back; very handy if the train departs from platform 3) and if you say when you are going there, maybe some forum members can say hello.
Don't forget the Rail Museum in York is in two distinct buildings, many people forget to visit the other half. Best of luck for your trip.
Also, you might consider a bus from York to Pickering to use the North Yorkshire Moors Railway.
If the NYMR are running to Whitby, one option for a good 'circular' day out could be a Class 68 hauled train to Scarborough, bus to Whitby (I think this is a double decker with good views), NYMR from Whitby to Pickering, bus from Pickering to Malton to pick up a train to York (or you can stay on the bus all the way to York).