The Sahara Sand Box was originally designed by Werner H Bartmes of Germany in 1983, and subsequently marketed by the Naef company of Switzerland.
Within the sand box is a piece of plastic containing a pattern of small holes. When the sand flows down through these holes, an extraordinary pattern appears in the sand that remains. In fact the sand box has two pieces of plastic, separated by a small gap. Each piece has a different pattern of holes. Place the sand box one way up and you get a picture in the sand; turn the box the other way up and you get a different picture!
There were a range of these made, each with a different patterns of holes inside, and thus each box giving a different pair of patterns in the sand.