Glenwood Springs might be a bit of a drive for you! Just east of there is a spectacular hanging lake, but it is quite far. I'm not sure why that popped into my mind, though it is high on my list to do eventually
Very close by is Daniels Park which has Bison and great views of the front range.
Highway 67 out of Sedalia (a bit north of Castle Rock) is a fun drive with lots of fun options - like Cheeseman Lake and Devil's Head (if it is open, it usually closes around Dec 1).
I'm sure we Colorado folk will come up with more.