At the risk of oversimplifying, let me suggest that there are essentially three activities for visitors to Colorado -- viewing the scenery, visiting historic and cultural sites, and participating in outdoor sports. While there are some visitors whose only goal is to explore prehistoric American Indian sites or historic mining towns, and perhaps hard-core skiers or hikers who are interested solely in pursuing their preferred form of recreation, the vast majority of Colorado visitors want a smorgasbord of experiences: This might include a scenic drive over a mountain pass, a visit to a small-town museum in a Victorian mansion, and a hike to a picturesque lake.
These are all driving tours and, in fact, a motor vehicle is almost mandatory for anyone who wants to explore Colorado. Visitors to Denver don't need a car, and if you're heading to a major resort to ski for a week you can be car-less, but many of the best destinations here require that you drive.
Colorado has a well-maintained network of roadways that will take you to most places you want to visit, although not always directly. Unfortunately, Colorado is a big state, with everything spread out, so you'll end up doing a lot of driving. One consolation is that traffic congestion, even in the cities, is not nearly as bad as in many other states. Services along rural highways are often limited, though, so be careful about checking fuel levels. Also, because of seasonal road closures, the tours that leave the Front Range are for summer use only, although parts of them can be adapted for winter use.
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.