Boulder, Colorado

Boulder sits where the plains run into the mountains, at the mouth of Boulder Canyon, with the Flatirons — a row of tilted sandstone slabs — standing over the west side of town. The city began in the fall of 1858, when a party of gold prospectors led by Thomas Aikins camped along Boulder Creek during the Colorado Gold Rush. Boulder itself wasn't much of a mining camp; the Aikins party laid it out the following year as a supply town, selling tools, food, and provisions to miners headed up into the canyons. That role gave it staying power, and at its first session in 1861 the territorial legislature designated Boulder as the site for the University of Colorado, which opened its doors in 1877 and anchors the city to this day.

What really set Boulder apart came later. In 1967, after the county's population had nearly tripled in two decades, city voters approved a dedicated sales tax to buy and protect open space — the first time residents of any U.S. city had voted to tax themselves specifically for that purpose. That decision shaped everything you see now: the green ring of foothills around town isn't an accident but the product of decades of land purchases, today totaling roughly 46,000 acres of city open space with more than 150 miles of trails. It's why you can walk from a coffee shop on Pearl Street to a trailhead in minutes.