My parents were friends with Tom and Marlies when I was growing up. Tom was an artist and Marlies was from Germany. They had two daughters, I think.
In 1969 they sent out a very unusual Christmas card:
The card was folded into several rectangles. Here’s the front:
When you open the card you see this greeting:
Open it again and you see this:
Finally, a 24″x28″ poster of the Hopp family in 1969 is revealed.