The Rocky Mountain Arsenal National Wildlife Area is a refuge in the middle of Denver that offers opportunities for hiking, wildlife viewing and catch-and-release fishing. But, only a small part of it is available for exploring at the present time; most of the site is still being restored to how it looked before the middle of the 20th century when the Plains Indians inhabited the land or it was used for pioneer farming.

In 1942 the U.S. Army started producing mustard gas, and later ner...