Magical Room and Bill Weasley

[Brittany]

No: HPFGUIDX 53743

Okeydokey, to disprove my own theory, I went back and read the BBC 
online interview, and this is exactly what Rowling says:
"Go straight into a certain room, mentioned in book four, which has 
certain magical properties Harry hasn't discovered yet!"
So, it can't be the antechamber off the entrance hall, because that 
is only mentioned in book one.  But I still think it probable that 
it is the antechamber off the Great Hall.

Brittany, who does not give herself points for intelligence