Al you have to do is to go into the mansion, go up the stairs, and (sorry i forget what room it is but...)when you find a room with a platform and a piano from hell get ontop of the platform. Do a wallkick off the wall facing the door by doing a single jump onto the platform and doing a double jump on the platform and off the wall onto the ledge above. Go through the door up there and go up the steps with the windows facing down on you. (hint: this is also the room with the secret room "eye-to-eye").

hope this helped you out!