What started the [SPOILER] at [SPOILER]?

Warning: This post contains SPOILERS and speculation for Game of Thrones season 8. Go no further than this Night King mug if you wish to remain unspoiled.

The Winterfell set at Moneyglass, Northern Ireland heated up in a big way this week, after the production set it ablaze. Here’s the video, so you feel pain and remember you’re alive:

So at some point in season 8, Winterfell burns. That raises the question: who or what started the fire? We have a few ideas, some of them expected, some of them not.