16. Play frisbee golf
You'll have to bring your own discs, but the Paco Sanchez course is 10 minutes from Downtown and is easy to access by bike, car, or light rail.
17. Enjoy nature at the Rocky Mountain Arsenal
The National Wildlife Refuge is made up of over 15,000 acres and is open every single day, except for major holidays.
18. Take an artsy photo of the Millennium Bridge
Seriously, it looks good from any angle.
19. See the views at Sloan's Lake
Get two totally different (and awesome) views from one park. From the East side, you can see the mountains and from the West, the Denver skyline.
20. Fishing at Wash Park
There are a few spots where fishing is allowed. If that's not your thing, there're 155 acres of park to explore.