September is an awesome time to visit Denver. The city is full of so many great things to do. My highlight was taking in a Broadway show at the Denver Performing Arts Center. The venue is wonderful. The cafes around town are limitless with my personal favorite being The Palm; terrific steak salad.
There is so much to do at night. The bar scene is extensive and my favorite restaurant was Guard and Grace. If you have a group I highly recommend the tasting room. Fantastic service.
However, my personal favorite place to visit was Red Rocks. It is an amphitheater to rival anything. A stage set between a huge rock structure that is mesmerizing enough to just stand and admire for hours never mind the acoustics and sound from the concert itself. The views of the mountains and the city skyline make for a one-of-a-kind experience.
If you get the chance add Denver of your cities to see.