When I was working at Friendly’s one summer, I came in to work and things were pretty slow. The store manager was in his office and several other people were crowding around him, staring intently at a strange looking poster.
I managed to break the gaze of someone and asked what it was all about and was told that hidden inside the picture was an underwater picture of fish and dolphins and a reef.
I believe the picture was called “Calypso Reef” but I haven’t been able to find it anywhere. However, in my searches I was able to find lots of interesting links about stereograms, or as some call them, SIRDS. I found a stereogram that looks similar to Calypso Reef, but the 3D image is different.
They’re old news now, but it’s still cool to me. Here’s a FAQ with more information about them.