I love December in York. Our friends all come up and we spend the weekend going out there a couple of weeks or so before Christmas.
Coney Street and the main thoroughfares are practically impassable on a Saturday. Sundays can be marginally better. There are lovely eateries just outside the main centre, which we now gravitate toward as for some years past getting in anywhere for a decent lunch has been a problem. The museums are wonderful. I like a walk on the Knavesmire, or round the city walls (as long as ice hasn't closed them off), or by the river. Monk's bar looks so beautiful all lit up at night. And I could spend all day in the old bookshops - which, aside from the one by the minster, you can actually get into, even in December.
I've given up on Christmas shopping as it's a bunfight but there's a whole other world to York. Last year was a bit weirder - the whole place was soggy owing to the major floods: we saw more than one car floating off from the riverside car park! But it's always worth visiting the railway and the castle museums, and I love retreating to the Museum Botanical Gardens with a good book (albeit not at this time of the year!).
Edited