I love running especially on the treadmill, it seems easier than running outdoors. I'm more likely to push myself on the treadmill because I can see the distance I guess. The great outdoors however, is a perfect source of fresh air and great to clear your mind because of all the sight you could potentially see, where as on a treadmill the most interesting thing to look at, is the person's back in front of you.
Running is great for lower body and cardio work out. Here is a 20 minute treadmill work out that is sure to get you sweating.