Take a drive or hike around the park viewing the spectacular mountain tops as the aspens change, try to spot an elk, moose or big horn sheep. And don't forget to stop at the Continental Divide.
If you prefer the water over hiking, you can boat, kayak, paddle board at the lake. There is also a boardwalk with shopping and restaurants to explore.
You can also explore the mountain on horseback or zip lining. Devils Thumb Ranch, a nearby resort, has a few different activities to choose from.
If you like golfing, Granby Ranch has a golf course with great mountain views. Or if you prefer fishing they also do guided fly fishing tours. The weather is perfect in September