There are sparrows in the United terminal at Denver International Airport. They survive a never-ending layover, jolted from their nest above B22 by booming "final and immediate" boarding calls. It's probably not a bad life -- heat in winter, easy access to crumbs and lots of space to fly.

While I'm no sparrow, I've survived many long layovers too. I imagine in 2005 that I spent the equivalent of four full days and nights sitting in airports. Truthfully, the longest layovers are the best. Last year I had a 13-hour layover in Honolulu, of which 12 hours was spent with my toes in the sand on Ala Moana beach. In March, during a four-hour layover at Dulles, a buddy and I caught the Hyatt Regency bus into Reston for a lunch. And just a few weeks ago, I had 8 hours in Munich. I enjoyed a shower and lunch in the Lufthansa Senator Lounge before whisking the S-Bahn down to Marienplatz for some Christmas shopping.

Of course, some airports, like Denver, which sits 30 miles outside of the city, are not amenable to such layover adventures. In such cases, it's best to have a charged iPod and have a taste for people-watching. Or sparrow-spotting.