Drive up to Rocky Mountain National Park. It is about one hour north and beautiful!
If you take the full loop you end up passing the casinos on theway back.
There is also great cheap horseback riding in Estes Park (name of city) at the entrance to the Park.
Go see the Red Rock natural theater outside of town.
If you want a nice day trip, go down to Colorado Springs. Garden of the Gds APrk is great!
I live in the Northeast and spend a week each quarter in Denver. Enjoy!