This is absolutely beautiful. There isn't enough fic that writes Hogwarts as a character, and you've done this marvellously. I feel like it is the castle talking, like this is the language that it would use, like this is the way it would understand the characters. And what a marvellous understanding that is.
(I think I might know who you are, too, though if I am right the pairing is completely surprising. Can't wait til reveals to see.)