Although it's possible to enjoy and explore Estes Park and Rocky Mountain National Park without a personal vehicle, having one will certainly help. We advise that you rent a car to get to Estes Park from Denver International Airport and also to explore the national park to the fullest. There are free shuttles in town and in the park that you can use if you want to save money, but you'll love the freedom afforded by having a car to explore this area at your own pace and on your own schedule.