The Shrieking Shack

Falsely rumored to be "the most haunted building in Britain," the Shrieking Shack is a favorite stop on any Hogsmeade visit. However, the wails that were once heard emanating from this creepy building were not in fact ghosts, but rather Remus Lupin transformed into a werewolf. The shack, in fact, was built when he came to Hogwarts, allowing him to transform a safe distance away from the other students. The shack cannot be broken into from the outside, though Fred and George have tried; it must be entered instead through a secret passageway, the mouth of which lies under the Whomping Willow.