I have stumbled across this great Japanese word: shinrinyoku, translated as "forest bathing". This is the act of going into a forest to immerse yourself in the greenery. Here is a Wikipedia article on this, and there is a website dedicated to this.
I personally have always had an almost overpowering sense of well-being and euphoria when walking through a forest (something that underpins my love of fieldwork in rainforests), This is something I have always attributed to a psychological response to being surrounded by the intricacies, mysteries and majesty of nature. There are some claims that there are direct (non-psychological) health benefits, with the immune system boosted by anti-bacterial volatiles emitted from trees, though I have not read enough to judge whether there is convincing medical evidence for this. If true, this would be a fascinating ecosystem service provided by woodlands and forests
Yadvinder Malhi is an ecosytem ecologist and Professor of Ecosystem Science at Oxford University