Running? Maybe not free, but shoes are a pretty reasonable price for admission. Great way to get out and see more of your city, trails, or even while you're traveling. Healthy and feel good endorphins are a bonus.

Photography? Yes a proper camera helps, but your phone has one. Third party camera apps can help make it more manual and learn the exposure basics before committing to an actual camera. Used ones can be had pretty cheap if you decide to pursue further. This can be a rabbit hole hobby costing thousands but doesn't have to be.