The Rocky Mountain Arsenal, or "The Arsenal" as we call it locally, is nearly 25 square miles of scenic wildlife oasis tucked between Denver International Airport and the north-east corner of Denver about 15 minutes from where I grew up. What was formally a WW2 chemical weapons facility has now been restored to a home for hundreds of native and migratory wildlife species and is free to the public to explore. Step back in time and see the pre-development high plains. In addition to the fantastic views of snow-capped peaks along the front range, common residents are bison, deer, coyotes, prairie dogs, raccoons, skunks, ferrets, hawks, eagles, herons, cranes, larks, blackbirds, geese, and many other bird species.
Despite it being free and right at the city's edge, it is rarely crowded. Try the scenic wildlife drive and audio tour, hiking, bike riding, fishing (for a small fee), and a fascinating visitor center. I intend to spend more time here over the coming seasons.
New images can be viewed in the Colorful Colorado Gallery.