If you have access to a set of stairs -- at home, at your office, at a local park, wherever -- then guess what? You basically have access to a makeshift gym.
And not a froofy, sissy gym, either. Stair workouts are killer because you have to carry your own bodyweight up an incline against gravity. It's brutal. And if you're the type who sucks wind after climbing a couple flights of stairs (don't worry, most people do), this workout is pretty much guaranteed to knock you flat on your back.
Not all of the suggested exercises are appropriate for all people, so go at your own pace and focus on the exercises you can do, subbing in basic stair climbing for the exercises you can't. Over time, you can work your way up to completing the whole shebang.