I found the below image on /T/BLOG/ over the weekend. This is a photoblog by T.J. Kemme.
I found when viewing this image that there was an optical illusion at play.
Due to the shadows curving around the columns I get the impression that this structure leans to the left. There is also the sense that the columns are spread wider at the top then they are at the bottom.
This image is of the sidewalk behind the Mountain View Civic Center in Mountain View, CA
The above columns may in part seem as if they aren't straight due to what is know as the Zollner Optical Illusion. The below image is a a series of eight vertical lines that are in fact parallel to each other. You can see how the slanted lines (similar to the shadows above) cause an apparent distortion of the image and the lines appear to tilt.