The people who know of this rooms existence are few and far between. But those of them who do know of it, would tell you that if you wish to access the room, you should pass the spot on the wall three times, thinking of the kind of room you would like, and, if done correctly, a door should appear, leading to your desired space. If you do it wrong, then you're stuck sitting with the painting of Barnabas the Barmy, trying to figure out what went wrong.