not know about are: A passage beneath the Whomping Willow, leading to the Shrieking Shack. A passage behind a mirror on the fourth floor, which is caved in. It leads to Hogsmeade, but it is not known exactly where. A passage beneath the one-eyed witch statue by the stairs to the Defence Against the Dark Arts classroom, leading to the cellar of Honeydukes. Speaking aloud the word 'Dissendium' to the witch allows access to this passage; the hump on the statue then opens and reveals the hidden passageway. A further link between two vanishing cabinets, one in the school and the other in Borgin and Burkes in Knockturn Alley presumably works until Chamber of Secrets when Peeves (persuaded by Nearly Headless Nick) smashes the Hogwarts cabinet. The passage is reopened in Half-Blood Prince when Draco Malfoy fixes the cabinet. This passage is not shown on the Marauder's Map as it is not part of the castle itself. Besides passages in and out of the school, there are also numerous short-cuts that lead from one part of the castle to another. These are often concealed in such fashions as a tapestry which hides a hole in the wall. Room of Requirement On the seventh floor opposite an enormous tapestry depicting Barnabas the Barmy attempting to train trolls for the ballet, the Room of Requirement appears only when someone is in need of it. To make it appear, one must walk past its hidden entrance three times while concentrating on what is needed. The room will then appear, outfitted with whatever is required. To the Hogwarts house-elves, it is also known as the Come and Go Room. Dumbledore is the first to mention the room, noting that he discovered it at five-thirty in the morning, filled with chamber pots when he was trying to find a toilet. However, Dumbledore did not appear to know the Room's secrets. Dobby later told Harry of the Room in detail and admitted to frequently bringing Winky to the room to cure her bouts of Butterbeer-induced drunkenness, finding it full of antidotes and a "nice elf-sized bed." Filch was said to find cleaning supplies here when he had run out; when Fred and George needed a place to hide, it would appear as a broom cupboard. Trelawney also makes a habit of using it to hide her empty sherry bottles after she is sacked in Order of