Training in stairwells provides for a great aerobic workout and helps build and strengthen those important leg muscles. Vary stride length (2 steps at a time), alternate your leading foot, and wear a light pack to increase the challenge. For the super keen, add push-ups, lunges and squats at each flat levelled area. Keep clear of doors opening suddenly, watch your step, no injuries please!
Short video: http://youtu.be/Ql3JE8RnzSE