This card looks complicated, but it’s just a basic 4 1/4″ x 11″ card base with an extra couple of folds. We added a panel inside for the view out the window. It folds flat and fits in a normal envelope, but pops up for dimension. The farther apart you put the folds, the deeper the view.
Click for supply list and printable directions.
Cottage Window Viewer Card 4-13-13