The caloric cost of walking, about 5 (k)cal/min; walking upstairs, 9 cal/min; walking downstairs, 7 cal/min, or, the average of climbing and descending stairs, 8 cal/min.
So, I naively go to McD's for lunch and get a doublecheesburger and small fry. Cha-ching, 690 frigging calories or about 86 minutes on stairs. Ouch. Remind me not to flip that menu again.