Depth Perception

I've always thought optical illusions are a pretty cool thing, but while it's one thing to manufacture them in drawings, it's another entirely, it seems to me, to enshrine them in sculpture. Here's a piece outside the McNay Museum in San Antonio that appears to have a great deal of depth when viewed from the vantage point of the museum:


Here's the view from the opposite side:


However, here's a side view that shows to what extent the depth you see from the front and back is mostly illusory:

I thought that was a pretty neat piece: the eye projects a lot more depth and complexity to the sculpture depending on your perspective. Here's another remarkable sculpture from the McNay - this one, if I'm not mistaken, from the late Austin sculptor Charles Umlauf set in the museum's fabulous courtyard: