By plane
Denver International Airport (http://www.flydenver.com/), IATA: DEN, ICAO: KDEN. Commonly referred to as DIA, it's about 18 miles northeast of downtown. Frontier Airlines, United Airlines, and Southwest Airlines all maintain hubs in Concourses A, B, and C respectively. Most other major domestic carriers also have service here.
Frontier Airlines
(http://www.frontierairlin...). Discount carrier with its hub at DIA's Concourse A and service to and from over 60 cities in the United States, Mexico, and Central America.United Airlines
(http://www.united.com/). The largest carrier at the airport, with service across the nation and the world from Concourse B.Southwest Airlines
(http://www.southwest.com). The quintessential discount airline maintains its fastest-growing hub in Concourse C.The airport is set amidst rolling plains with the towering Rocky Mountains and Denver to the west. DIA is somewhat far from any conceivable local destination. The public transportation service SkyRide (http://www.rtd-denver.com...) offers 5 bus routes from the airport with several stops each, delivering you to many "Park and Ride" locations in the metro area for $9-$12 one way. Purchase tickets at the RTD desk in the main terminal. The airport can be crowded due to a post-9/11 security redesign that created a single central screening station, followed by a train that passengers must take to Concourses B and C. It can take up to an hour to get from the ticket line to the gate, so travelers should get to the airport at least 1.5 hours before their scheduled departure time. There are a number of airport shuttles you can take from DIA to the city and destinations in the mountains.
Private pilots mostly fly into Centennial Airport ICAO: KAPA, south of town not far from the Denver Technological Center, and Rocky Mountain Metropolitan Airport ICAO: KBJC, northwest of town near Interlocken Business Park, Broomfield and Boulder - and the closest airport to downtown Denver. On warm days the density altitude may make takeoffs difficult; Centennial and Rocky Mountain Airports thus have relatively long runways, to accommodate volumes of private jet traffic. Flight visibility in the Denver area is often in excess of 100 miles; weather fronts tend to travel quickly N-S along the front range. For small planes, any direction but west is a good choice.
Amtrak'
s (http://www.amtrak.com/) California Zephyr stops in Denver once a day, continuing east to Chicago and west to Emeryville, California. Union Station, where the trains normally stop, is currently undergoing renovations; a temporary station has been set up at Wewatta and 21st Street, across the train tracks from Coors Field. To get to downtown from the station, head down Wewatta Street along the railroad tracks past Union Station to 16th Street - there, you can cross the tracks into downtown.
Greyhound
(http://www.greyhound.com) The bus station is downtown at 1055 19th Street, just a few blocks away from Coors Field and other central attractions. Serviced by Greyhound and skyRide buses, the station also has storage lockers that can be rented hourly. Expect the bus station to be crowded and dirty.