Spent family vacation in Colorado this year. Not only are the national parks great so are the city parks. Garden of the Gods in Colorado Springs and Red Rocks are both amazing free city parks.
We went to Rocky Mountain National Park and saw much wildlife. One frustrating parts was the reservation system; we attempted to enter the park on west side at 10am; and had a reservation for bear creek on the east side at 2pm. We were told by ranger that we would not be able to enter park until an hour before the reservation and it would take an hour to just drive from west entrance to bear creek on East side. I nearly lost my shit after hearing that. Anyway it worked out fine but was very frustrating at the time.
We also drove to Great Sand Dunes NP, this was a long day in the car, and the park is located in the middle of nowhere. However it was well worth the drive, as the landscape at the park is otherworldly