Sometimes, all too often, my schedule makes it difficult to get in my 5-mile-daily-minimum exercise (power walking). Why it occurred to me at this late date I don't know. Since many of us, post 9/11, get to the airport early, there is a matchless opportunity to log an easy mile or so of decent, borderline aerobic exercise.
Many of you have been to the Atlanta airport, I suspect. You ride an underground tram to your gate. You can, in Atlanta and several other airports, walk if you wish. Yesterday I left from the B concourse, but I walked from security out to the end, the E concourse I think, and then back to B. As I casually measured it, I logged about 1.25 miles ... at a very brisk pace further enhanced by carrying a heavy backpack and pulling a roller bag. Even in smaller airports (e.g., Nashville, recently) I've discovered that if you "do" every concourse from end to end, and maybe but no more than twice, it's pretty easy to log a mile while receiving only a few odd glances. You get in some pretty effective exercise, relax pretty effectively from a perhaps stressful day ... and the only price I've found is being a little sweaty for a few minutes when you're done.
(To state the obvious, on longer flights I am a big, big advocate of the in-seat stretches! Most airline mags offer rather complete suggestions—and hats off to British Airways for the best "program," in my opinion.)