I learned about it on this Tim Ferriss podcast. They mentioned a couple great resources from Time and a book by Dr. Qing Li called "Forest Bathing: How Trees Can Help You Find Health and Happiness"

It resonated with me, I grew up in a rural area and spent hours and hours in the woods from a very young age until I left for university. Since then I have been spending more time wandering the various paths around where I live and have noticed a real benefit to my mental health.

Maybe a real thing, maybe not, but walking and fresh air can't be a bad thing.