Estes Park is a nice small touristy town in the Foothills about 1.5 hours Northwest of Denver. From there you can go to Rocky Mountain National Park, which is beautiful and has tons of places to hike. The hiking can be kind of iffy at the end of October if it's snowed and the trails have gotten muddy, so keep that in mind. Trail Ridge Road (the highest continuous paved road in the United States) will likely be closed but it is a pretty cool drive! I don't recommend trying to do the whole thing over the continental divide, it takes forever, and then you'll find yourself on the wrong side of the mountains!
Fort Collins has the famous New Belgium Brewery, where they make Fat Tire beer. They give tours there, but you have to schedule it in advance. Old Town Fort Collins is a nice stroll to see the shops and eat at some pretty good restaurants. Disneyland's Main Street is modeled after Old Town Fort Collins, how cool is that??? The Colorado State University campus is a pretty walk, especially the Oval and the Annual Trial Gardens. If you like to ride bikes, there are a lot of paved trails all through Fort Collins and Loveland with nice views. There are several locations in Fort Collins near Old Town that have bike rentals.
That's all I can think of at the moment! Hope you have a great trip!