How about draw 3-D things on the sidewalk because they're just cool to look at?
Yeah, that's what I'd do, too.
These are the creations of Julian Beever, a sidewalk artist who has drawn with chalk for over ten years all over the globe. He makes 3-D looking images that are truly mindboggling.
*This drawing was done in Tokyo for the TV show 'Unbelievable' and was a plea to Japan to appreciate the beauty of living whales.
But you have to look at them from the right direction - just look at this lobster one from right the wrong angle:
Anyhow, I just thought they were cool. And they're nature-inspired, so they sort of fit.
Here's the best one I've seen so far - it actually took me a minute to realize it was drawn: