Denver

Denver needs 2 days: the Denver Museum of Nature & Science on one, Red Rocks Park -a natural amphitheater carved into red sandstone formations, one of the best outdoor concert venues in the world- on the other. May-September has the best weather for the nearby mountains. It's cheaper than coastal cities, though prices have risen with the last decade's tech boom. It's known as the «Mile High City» for sitting exactly 1,609 meters (one mile) above sea level, and it's the classic gateway to the Rocky Mountains, less than an hour from several world-class ski resorts.