fictional holidays

Since I am at present avoiding content (I have discovered, I suppose, the unfortunate art of staying sane by lack of analysis) and avoiding one of my weirder errands of the week (I have to go buy feathers).

Talk to me of fictional winter holidays.

Currently there's The Longest Night from Kushiel's Dart on the list, and Last Night from the Swordspoint universe. Yes, and Festivus from (did this come from Seinfeld?). What else have you've got for me. Because I'm so over, you know, the actual holidays.