I have included links below to a number of resources related to research on the health benefits of spending time in nature.
Recent research studies
The urban brain: Analysing outdoor physical activity with mobile EEG (British Journal of Sport Medicine)
Hiking Makes You Smarter (Backpacker Magazine Article)
Hiking May Increase Creativity (WebMd)
Wanderforschung (German for Hiking Research)/Dr. Rainer Braemer