Enter a room located snugly inside the "empty" corridor. It's a plain, white-walled room with absolutely no furniture at first glance, but right in the middle is a small object, a trashcan. In truth, it is a portkey, and it will transport you to, well, noone knows exactly where it is, but it is a mall, a wizarding mall. It has lots of muggle shops, but noone save wizards and witches who reside in Hogwarts can actually go there....