5 Best Cities for Being Thin

"It all goes back to your social network," he says. "If you're in a close community -- a college town -- people tend to go out running together or climbing together or a lot of other things."

As for housing, Boulder has a median asking price of about $370,000, up 5.9% over the past year.

There are some 12,000 Boulder-area houses and condos listed for sale on Realtor.com, priced from $35,000 for a one-bedroom condo to $3.7 million for a six-bedroom estate.