You know the blue top open concept counter between the livingroom and kitchen of the Cunningham house.Inspite of the swinging door on the side of the counter,the camera has often revealed a completely open space on the other side of the counter.I suppose that was the side that us TV viewers weren't supposed to see.Because everyone always used the swinging door.

That weird open area was actually the beginning of the Nebulous Void that was also located in Arnold's on the other side of their booths.

From the Happy Days characters' points of view it was just a mysterious smoke-like haze that they would often think about in wonder when after they went to bed.