Code golf [0] can be a fun outlet if you want to learn a new angle of something you already know. Similarly, I've recently taken to building extensions for things, e.g. a simple utility for Chrome [1], since it allows you to go from nothing to something useful super quickly. Outside of coding, any form of art is beyond liberating — music, dancing, photography, etc. You use your mind in a completely different way and it feels like a fresh breeze blowing through the hallways of your head.

[0] https://codegolf.stackexchange.com/

[1] https://github.com/Etheryte/right-click-opens-link-in-a-back...