I have seen a few versions of the "Impossible " card, in different sizes,
but they all work on the same principle -
the card is made from one piece of card - in my example its 7" x 5"
and the card folds completely flat for posting!
Here's my first attempt
|Card folded flat for posting|
|Side view showing mechanics|
If you fancy a go at this, there are loads of videos on youtube that you can follow-
If I can do it - anyone can!!