In May 1956, M.C. Escher finished his lithograph Print Gallery. In a letter to his son Arthur he wrote about this lithograph:
"The odd print I told you about last time is finished, though not yet printed. I don't think I have ever done anything as peculiar in my life. Among other things, it shows a young man looking with interest at a print on the wall of an exhibition that features himself. How can this be? Perhaps I am not far removed from Einstein's curved universe".
In Escher's original work, he left a blank space in the center. See how this spiral was continued using the Droste Effect.