I love play with perspective and the space as we know it: Thus M.C. Escher has to be mentioned.
(
"Relativity")
Then, there is the mechanical side of things; although not all will be considered art by all, I'd suggest checking out Theo Jansen's Strandbeest, which is not a single creation but a group of them:
http://www.strandbeest.com/
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On my own art, there isn't much to be praised, but for the bonus challenge I'll take part;
This isn't the original version of this work, originals were on paper. I call it just "Bird", from a larger project of the same name. My aim was to offer a good look at how birds are constructed. This is supposed to be from below the bird, flying over with the wings wide open. You should see the correct arrangement of flight feathers, as well as the skeleton and body. Although somewhat lacking, I was and still am quite proud of it.