From Wikipedia Picture Of The Day; November 6, 2013:
A mandelbulb is a three-dimensional analogue of the Mandelbrot set, a mathematical set of points whose boundary is a distinctive and easily recognizable two-dimensional fractal shape. This image, for the iteration z ↦ z8+ c, is rendered with a volumetric ray tracing and path tracing global illumination algorithm in the Corona renderer. It took about 70 hours to completely render.
Image: Ondřej Karlík