If hearing the term nature-deficit disorder concerns you, then this brainstorm book of solutions for integrating more of the outdoors into your life is easy to read for those suggestions that apply to your life, and skim over those sections that don't.
If you want to know more about the research behind nature-deficit disorder, then check out the Research Library at the Children & Nature Network.
Richard Louv has written two other books on this subject as well. Last Child in the Woods: Saving Our Children from Nature-Deficit Disorder focuses on readers concerned with the impact of nature-deficit disorder on children, while The Nature Principle: Human Restoration and the End of Nature-Deficit Disorder is geared toward helping adults.
As a child-free minimalist, I found many inspiring ideas and stories here.