1952 wood-engraving by M.C. Escher
, measuring 32 by 34 centimetres.
"However much this dragon tries to be spatial, he remains completely flat. Two incisions are made in the paper on which he is printed. then it is folded in such a way as to leave two square openings. But this dragon is an obstinate beast, and in spite of his two dimensions he persists in assuming that he has three; so he sticks his head through one of the holes and his tail through the other."
You can see this engraving (known in its original Dutch as Draak) by searching Google Images for "Escher"+"Dragon". I once provided URLs, but they expire; this technique should remain effective for quite some time.