Imagine a particle in the complex plane, starting at $c_0$, a Gaussian integer, moving initially $\pm$ in the horizontal or vertical directions. When it hits a Gaussian prime, it turns left $90^{\circ}$.

@online{item15,
title = {Gaussian prime spirals},
author = {Joseph O'Rourke},
url = {http://mathoverflow.net/questions/91423/gaussian-prime-spirals},
urldate = {2012-03-24},
abstract = {Imagine a particle in the complex plane, starting at {\$}c{\_}0{\$}, a Gaussian integer, moving initially {\$}\pm{\$} in the horizontal or vertical directions. When it hits a Gaussian prime, it turns left {\$}90^{\{}\circ{\}}{\$}.},
comment = {},
collections = {Easily explained},
year = 2012
}