(Image: - Own work)
The Mandelbrot set is a two-dimension set that is described by a relatively simple equation, yet it produces a very complex design. In 1980, Benoit Mandelbrot made high-quality visualizations of the set, named after him, while working at IBM's Thomas J. Watson Research Center. Quantamagazine published a very thorough history of the study of the Manelbort set. In that article, a YouTube video was included that explores its un-ending complexity and many interesting features.
You can view it here: A Long Zoom Into the Mandelbrot Set.
I also recommend this video: The Mandelbrot Set.