The Room of Requirement can only be found by someone in desperate need. One must walk around the corridor three times, passing a portrait of Barnabas the Barmy, all the while concentrating on what he or she needs the most. When the room reveals itself, it will contain the solution to that need. Dumbledore's Army used this place to practice deffensive spell when not permitted by the ministry in Harry's 5th year of 1995.
