Sneak in some exercise

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When I was lucky enough for a staycation last month, my weight crept up a bit. Then went back to work, [insert magical harp sound here] it restabilized at its lower average. The difference? Three sets of stairs in my daily commute.

They left me a little winded the first few days back, but now I can climb them and sing like Julie Andrews (in my head, of course.)

Are there any ways you sneak in extra exercise, or could add a bit more?