Research and note-taking.
Writing a fantasy book where one of the towns nearby is one of the central places in the story provides a great deal of exciting research opportunities. One example is the folks who own this one very fine restaurant. The restaurant, which incidentally has wonderfully delicious food, is the location where my characters meet a lot. I confess that every once in awhile I don't really need to research their excellent dessert selection all that much, but you know, I need to be familiar with just how wonderfully delicious that Tiramisu really is, because as one of my characters Pistachio the Pirate's favourite dessert it's not optional to describe just any Tiramisu. As a result of this "Research" we've actually managed to strike up a bit of a friendship with the folks there. Taking notes can be a very fun and good tasting experience.
I do other things less interesting things besides that, such as spell checking, but in the end it's those little things like making notes on Tiramisu that make writing fun.