Stairs are everywhere, of course, but they are rarely embraced as an option for getting into shape. They wait in the stale air wells of high-rises (especially in dense urban centers like New York City), or on stationary machines in the corners of health clubs now inundated by the more popular, but less strenuous, elliptical machines. Many stairwells aren't even accessible, often because of post-9/11 security concerns. But when they are, or are opened especially for runners going up, they provide a workout that returns maximum value in minimum time, with low impact. And going up is much better for your knees than going down.