"Oh, I would never dream of assuming I know all Hogwarts' secrets, Igor" said Dumbledore amicably. "Only this morning, for instance, I took a wrong turning on the way to the bathroom and found myself in a beautifully proportioned room I have never seen before, containing a really rather magnificent collection of chamber pots. When I went back to investigate more closely, I discovered that the room had vanished. But I must keep an eye out for it."