In this Illusion, the Vertical lines in the above figure are Parallel, but appear to be tilted at an angle.
See also Illusion
References
Jablan, S. ``Some Visual Illusions Occurring in Interrupted Systems.''
http://members.tripod.com/~modularity/interr.htm.
Pappas, T. The Joy of Mathematics. San Carlos, CA: Wide World Publ./Tetra, p. 172, 1989.