Julian Beever's optical illusions

What I find most interesting about these optical illusions, apart from the fact that they're great, is that even though you know they are illusions, you can't help but be caught into the phenomenological trap Beever is setting. In other words, as long as you're looking at the pictures, even knowing full well that they are just two-dimensional pictures, they totally look real and three-dimensional.

Here is a challenge for you: can you picture in your head what these images would look like from straight above? I bet it's probably as difficult as trying to see one depth version of a necker cube while you're looking at the other.