Assuming that you live in an area where bicyclists aren't in serious danger of injury or death from aggressive, inconsiderate motorists, this answer is just great! Bicycling is great exercise, and it doesn't pollute the air. It's also much faster than walking, so it does expand one's horizons somewhat. Riding a bicycle is too dangerous where I live, so I don't even own one, but how I wish I could ride a bicycle regularly!
You probably thought I was a hopeless conservative by now. <g>