Leaving illusions behind, heading home to Seattle for a bit. Here's  a wonderfully ugly picture, redeemed by the fact that it is also a subtle illusion.

It looks as though the orange surface is at right angles to the observer (i.e.flat on) but it's actually at better than 45 degrees. The reason it looks flat is because the light washes out any shadow or variation in color or texture. It was taken late in the afternoon, the sun transforming the wall into pure color, transforming our perception along with it. An image obscured by light, contrasting with this one, an image revealed by shadow.