I studied mathematical optimization in school and can still be nerd sniped (XKCD) by an interesting problem.
I like playing music. I learned classical piano and cello as a kid and now I relax by playing pop/jazz styles on the piano, because I like the freedom to improvise and create your own arrangements.
I enjoy entertainment most in a cosy environment with a small group or alone, so for movies and music I'll usually watch or listen at home. When going out I like nature (parks, beaches, light hiking, etc.). Indoor rock climbing is fun because it turns exercise into a puzzle game.