Boulder is a city of 100,000, elevation 5,400 feet (1650 meters), located thirty miles northwest of Denver. It's just under an hour's drive from Denver International Airport, known here as DIA, though its official airport code is DEN. It's also an hour's drive to Estes Park, gateway to Rocky Mountain National Park. Boulder is surrounded by a wonderful greenbelt with 120 miles of trails. The Front Range of the Rocky Mountains rises on the west side of town. The entire region is a paradise for hiking, cycling, rock climbing and almost every kind of outdoor activity except surfing.