The second floor has what you might call classic Escher: the metamorphoses and impossible buildings, and hands drawing each other. All of which is copyright, obviously.
But our favourite bit was the top floor with all the interactive stuff. The cube is painted on the walls - some around the doorway, some in the room behind.
Best of all was the room-within-a-room with trick perspective. The left hand side is actually smaller and closer to the camera. You have to pay extra for a photo, and I usually regret paying for that sort of extra, but we all love this.