re: Desk-jobbers, how do you stay active at work?

I would love to be able to take the stairs in my building since I work on the 14th floor but once you enter the stairwell you can't gain access to any door except the bottom one. It's emergency only. I try to go walk around the block a couple times a day. I figure if people are taking 6-10 cigarette breaks a day I can go for a 5-10 minute walk.