Since most visitors to Colorado will probably be traveling between cities and also into surrounding areas, you will most likely want to rent a car. However, you can save a bit of cash by doing your downtown city exploring, which can be done quite conveniently using public transportation, at either the beginning or the end of your stay, and only renting a car when you plan to leave town.
Each of the individual city reports contains information on car rentals and public transportation. A good first stop: Denver's largest map store, Mapsco Map and Travel Center, 800 Lincoln St., Denver, CO 80203 (tel. 800/456-8703 or 303/830-2373; www.mapsco.com), offers USGS and recreation maps, state maps and travel guides, raised relief maps, and globes.
In Colorado in general, the most cost-effective way to travel is by car, but Denver, Boulder, and Colorado Springs have pedestrian- and bicycle-friendly routes and at least decent public transportation.
If you're visiting from abroad and plan to rent a car in the United States, keep in mind that foreign driver's licenses are usually recognized in the U.S., but you should get an international one if your home license is not in English.
Check out Breezenet.com, which offers domestic car-rental discounts with some of the most competitive rates around. Also worth visiting are Orbitz.com, Hotwire.com, Travelocity.com, and Priceline.com, all of which offer competitive online car-rental rates.
Although you can fly between Denver and Colorado Springs, it's not nearly as economical as driving the 70 miles. Overseas visitors can take advantage of the APEX (Advance Purchase Excursion) reductions offered by all major U.S. and European carriers. In addition, some large airlines offer transatlantic or transpacific passengers special discount tickets under the name Visit USA, which allows mostly one-way travel from one U.S. destination to another at very low prices. Unavailable in the U.S., these discount tickets must be purchased abroad in conjunction with your international fare. This system is the easiest, fastest, cheapest way to see the country.
Although you can catch an Amtrak train from Union Station in Denver, it's not a particularly good method of travel between Denver, Boulder, and Colorado Springs -- not until a light-rail build-out takes place in the next decade, at least. In Denver, existing light rail is useful for navigating certain attractions.
International visitors can buy a USA Rail Pass, good for 15 or 30 days of unlimited travel on Amtrak (tel. 800/USA-RAIL [872-7245]; www.amtrak.com). The pass is available online or through many overseas travel agents. See Amtrak's website for the cost of travel within the western, eastern, or northwestern United States. Reservations are generally required and should be made as early as possible. Regional rail passes are also available.
Bus travel is often the most economical form of public transit for short hops between U.S. cities, but it's certainly not an option for everyone (particularly when Amtrak, which is far more luxurious, offers similar rates). Between Colorado Springs and Denver, the Front Range Express (tel. 719/636-3739; www.frontrangeexpress.com) offers bus service for $9 one-way. Greyhound (tel. 800/231-2222; www.greyhound.com) is the sole nationwide bus line. International visitors can obtain information about the Greyhound North American Discovery Pass from foreign travel agents or through www.discoverypass.com; it provides unlimited travel and stopovers in the U.S. and Canada.
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.