Whether you need a rental car in Denver depends almost entirely on whether your trip stays in the city or heads into the mountains.
Downtown Denver Does Not Need a Car
LoDo, Union Station, Coors Field, and the 16th Street Mall are all walkable, and the A-Line train handles the airport connection. RTD light rail covers a fair amount of the rest of the metro area if your trip stays urban.
The Mountains Are a Different Story
Rocky Mountain National Park sits about 90 minutes from downtown, and ski resorts like Breckenridge, Vail, and Winter Park all require a drive along the I-70 mountain corridor. If any of this is on your itinerary, a rental car (ideally with all-wheel drive in winter) is close to essential, and public transit will not get you there practically.
Plan Around I-70 Traffic and Weather
The I-70 corridor sees heavy weekend congestion during ski season and can close temporarily during storms. If you’re driving to the mountains, weekday travel and checking Colorado road conditions before you leave will save real time.
Compare rental rates above if the mountains are part of your Denver trip, or check flight and hotel options if you’re keeping things downtown.