This is a little mysterious level in the game Chamber of Secrets. The entrance to it is in the living room of Gryffindor. But … He is behind the door, which is always closed. The small file to be added to one of the game folders corrects the situation.
As it became known, the owners of the disc with demonstration materials could unlock this level: if you start the shell of such a disc, then it hides behind one of the doors function that adds the desired file to the installed copy of the game.
The level itself can be seen in this video: