For a sustainable -- and just plain enjoyable -- way to get around, look no further than a bicycle. You can cover a lot of miles with just two wheels, but you won't be making the carbon footprint you would be on four wheels. Here are the top three U.S. cities for biking, according to WalkScore.com.
Minneapolis, Minnesota Bike Score: 79
Perhaps it's the frigid winters that bond the bike couriers, road racers, BMXers, and recreational cyclists in Minneapolis, Walk Score's winner for bikeability in the United States. If you're visiting, the Grand Rounds trail nearly circles the entire city, while the Mississippi River Trail follows both sides of the river, to name just two big routes. Learn more about the bike scene in Minneapolis here.
Portland, Oregon Bike Score: 70
Often considered the cycling capital of the U.S., Portland is a leader thanks to bike lanes, low-traffic bike boulevards, off-street paths, bike parking corrals, and a very lively bike culture. While you're there, combine two of Portland's loves -- beers and bikes -- with a Brewcycle tour (a 15-seater bike contraption that goes from brewery to brewery) or a Pub Peddler Brewery Tour from Portland Bicycle Tours.
San Francisco, California Bike Score: 70
One of the must-do activities while in the City by the Bay is to rent a bike along the waterfront and pedal across the Golden Gate Bridge to Sausalito. The views both approaching the bridge and from among its orange-hued towers are spectacular on a clear day (and the good news is that the wind cooperates with you on the way back, so it'll be comparatively easier pedaling). Try San Francisco Bicycle Rentals or another of the many shops around town for a good cruising bike.