If you are feeling fit and want to get away from crowds, enjoy one of the hikes that takes you further back into Rocky Mountain National Park. Most of these hikes will take you much of a day to get up there and back.
Long Hikes in Rocky Mountain National Park
For more challenging hikes check out Hiking Rocky Mountain National Park: The Essential Guide. In has 27 long hikes that will take you into gorgeous places throughout the park. It also contains 45 shorter hikes for those days you want to take it a little easier.