The mode of exercise the subjects of virtually all the large-scale, longitudinal studies on exercise and longevity engaged in was walking.  Consistent moderate exercise  performed over the lifespan - like walking - reduces the risk of lifestyle diseases such as cardiovascular disease, hypertension, diabetes, and certain cancers including colon and breast.  If you like in a walkable urban environment, such as downtown Toronto, make a point of using walking as a mode of transportation.  If you do not, schedule in daily walks of 20-30 minutes duration for thinking, reflecting and problem-solving.  Your mind will like it, and so will your body.

An early-morning walk is a blessing for the whole day. ― Henry David Thoreau

All truly great thoughts are conceived while walking. ― Friedrich Nietzsche, Twilight of the Idols, Or, How to Philosophize With the Hammer