alekth on 17 February 2010
I think you're supposed to see it as a 3D object, while it's 2D (well, ignoring the thickness of a steel bar).Though people usually expect something crazier when something gets called an optical illusion.
Not sure I'd be able to perceive it as 3D though, if I was there and walking around it. And maybe anyone trained in some modelling/architecture will perceive as 2D after seing three photos with different angles not affecting what you see.
