Are there any towns in the United States that bicycle is the only preferred transportation? If not towns, then parks (not bike trails, but like...a park that at least mimics a town setup)?

I like to dream, but this would be awesome for a great vacation getaway, or even an ideal place to live. In my area we have a place called "bicycle town" but it's only 1-2 miles worth of road meant for teaching the kiddies the rules of the road and cycling safety. If there was an adult version that was 20+ mile version, it'd be a cyclegasm.

So, any towns/parks in your area that are kind of like what I described? How about outside of the US?

Mackinac Island, in Michigan has only a few public service and commercial motor vehicles so most transportation is by walking, bicycling, and horse-drawn wagons. But walking is far more popular than bicycling. It's only about 4 square miles, but I'd guess the sum of all streets and paths probably gets up to your suggested 20 mile length.

Oh sweet, I'm not too far from Michigan either. Definitely googling this one. Thanks!

Isla Vista, California is pretty solidly bike friendly. UC Santa Barbara next door is a Gold Level Bicycle Friendly University. Isla Vista is mostly student housing so in the summer it's pretty laid back.

I.V. is right on the Pacific coast. The refugio oil spill is several miles up the coast though. There are cars there. If you are feeling adventurous, you can get out to Santa Barbara and environs, though the airport is right next to the university.