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The Mandelbrot set refers to a set of equations that create fractals, the patterns that occur in clouds, coastlines, mountain ranges, brocolli, spiral galaxies.
These two pictures were grabbed from Mandelbulb, a site devoted to three dimensional fractal imagery. These are not images taken from nature, but rather mathematical constructs that closely mimic natural forms. Cool, huh? There are a bunch more at the site I linked to above.
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One of the cool things about fractal images is that look pretty much the same no matter what magnification you are looking at. Double the size, triple the size, centuple the size, it all looks similar. Here's a "fly-by" on a three dimensional fractal. I believe the word you are looking for is trippy.
Thanks to the always interesting Bad Astronomy for pointing out the site.