Walking is a moderate-intensity aerobic activity. It is recommended that you get 30 minutes of aerobic activity on most days. Walking is good for your heart, lungs, and circulation. Crunched for time? Make lunch "hour" a half hour, and use the remaining time for a brisk walk.
Step it up:
On your 30-minute walk, mix in running intervals. Walk for five minutes, and then jog for five minutes.