Take up something you enjoy. If you don't like it, it will be a drudgery and you won't stick with or excel at it. Try some different things to see what works for you.
Racquetball, basketball, softball, tennis, volleyball, fencing, judo, karate, golf, horseback riding, jogging, track, bicycling, skiing, bowling, archery all come to mind quickly. Look around and see what's available to you, and what your budget allows.