Stair after Escher, photo by Harold Davis. View this image larger.

Here’s another Photoshopped version of the spiral staircase in Embarcadero Center. This original was with my Nikon 10.5mm digital fisheye. I varied the iterative technique by flipping the image to get the symmetry.

The image reminds me a little of an impossible M.C. Eshcer staircase.