A set of four greeting cards, plus envelopes. But these are quite special cards!
Each card is supplied flat, but when you squeeze the top and bottom edges together slightly, the card flexes and opens up. When you hold the card up to your eyes and look inside, you see a 3D version of an Escher illustration. Squeezing the card slightly allows you to adjust the focus.
Each card has a different illustration. They are 1) Ascending/Descending 2) Reptiles 3) Still-life and Street and 4) Bond of Union.
The cards are 14.5 x 10 cm when flat, and each card has two integral lenses.