Where you keep your cube.
At Mad Genius, Cedar Sanderson has a good post about using fractal based procedural art generating programs: https://madgeniusclub.com/2017/04/15/cover-art-fractals/
The software she uses is http://apophysis.org/ which is a freeware app for Windows.
My messing-about machine is a Mac and unfortunately, Apophysis isn’t available for Macs (and I don’t have room for a Windows partition on this machine). However, Chaotica does some lovely things and a free version is apparently available.