Theory on the book 5 cover:

Apparently, Mary GrandPre (the US illustrator) was the only one of the three illustrators to read the book before she drew the cover picture (the others were simply told: 'Draw this.') Therefore, her cover is the only one we can pick up clues from. I've formulated this theory:

- From an interview with JKR (read it here):

Question: If you could travel to Hogwarts for an hour, what would you do there?
Answer: 'Go straight into a certain room, mentioned in book four, which has certain magical properties Harry hasn't discovered yet! '

Well, firstly, in trying to figure what what that room could be: We know it's circular (like it's shown in the cover) and is only 'mentioned' so it can't Dumbledore's office because that's in book 2 as well and its more than just mentioned ...

So what about that room Dumbledore talks about to Karkaroff during the Yule Ball: '...Just the other day on my way to the bathroom I stumbled upon a beautifully proportioned room full of chamberpots , but when I attempted to find it the next day, it had disappeared, perhaps it only appears at the quarter moon, or at 2'o'clock in the morning or when the seeker's bladder is exceptionally full.'

I thought this was just a joke but maybe it's more than that. He describes the room as 'beautifully proportioned' and you can't get much more beautifully proportioned than a cricle. And notice that Dumbledore needed the bathroom (i.e toilet) and found a room of chamber pots - sort of what he needed! So what if the room gives you what you need (even though that sounds too much the mirror of Erised) or something like that so that Harry maybe needs something behind those cupboards or doors with mist coming out of them??? Well, I haven't completely worked it out and it may be nowhere near the truth but it's something.

Have anything to add? Email me.

ps: Notice the mistake on this cover? Harry has his wand in his left hand!