Not sure what you are up for, but a walk down the Pearl St. Mall in Boulder is always a favorite (only about 25 minutes from downtown to downtown) I will also echo the thoughts that Rocky Mountain National Park is worth the hour and a half or so from Denver. We get the annual pass every year and can't come close to seeing everything. Trail Ridge Rd. in the park is awesome. Timing it late in September could also result in seeing some Big Horn Sheep (State Animal). To be completely honest though, even the Front Range foothills are going to be awesome to see if you are not used to seeing mountains. Most of the snow has left the peaks anyhow, but there's a chance you'll catch some at the end of September. Cherry Creek is good family fun, mall with some restaurants, couple good bars, that sort of thing. Also, not sure what days you are going to be in before/after the series but if you time it right the Great American Beer Festival is the 24-26.