When we lived in Omaha we made the trip 3 times - some of our best Hokie friends live in Longmont. We went to see the Avett Brothers at Red Rocks one of those trips. Rocky Mountain NP is a great place, lots of wildlife. Tons of hikes, breweries, awesomeness. Enjoyed a Rockies game one trip. Red rocks, as is said below, is closer to Golden and thus Boulder and Colorado Springs. Boulder might be a good launching point, although expensive. The Coors tour in Golden is supposed to be fun, but I've never been. One of the best Hikes I've ever been on is Hanging Lake, but it's a fair drive on the other side of the mountains. https://www.alltrails.com/trail/us/colorado/hanging-lake