An enormous castle with non-Euclidean architecture and swarms of wizards and students.
And I ponder the supplies -- particularly the groceries.
Kind of important because my main characters are wizards, and on one hand, I need to define the limits of their powers to enable a story, and on the other, there's going to be some significant conjuring in the tale (of clothes and furniture actually -- long story) and this is as good a place to slither it in as any. . . .
Limits, limits, limits. Why is the castle not a cornucopia that can feed all the land?