The Room of Requirement

A magical room on the seventh floor of Hogwarts castle, the Room of Requirement appeared when students were in particular need of it and would provide whatever was required. Also known as the Come and Go Room, and Room of Hidden Things, it could be used for anything - from hiding or storing items to providing a toilet in a time of need. The Room was accessed by walking past the stretch of wall opposite a tapestry, featuring Barnabas the Barmy's attempt to train trolls as ballet dancers, three times concentrating hard on what one needs. The Room came into use on a number of occasions including as a secret meeting place for Dumbledore's Army.