I lived in Fort Collins for quite a few years. Used to love riding from Fort Collins up Highway 14 all the way to Steamboat Springs and back. Highway 14 is an incredible ride.
Also if you are in Denver it's worth the short ride up to the top of Mt. Evans. About 60 mile ride but you get to top out at 14,240 feet. The highest paved road in the continental USA. I have ridden it on my bicycle from Idaho Springs.