When I'm outdoors and active, I am so much happier. If I am on a multi-day outdoor trip to hike or rock climb, I feel like a completely different person. This is especially true on long trips that last more than a week. I have much less stress. I smile compulsively, instead of baring my usual strained expression. I have more energy. You might think at first that is simply because I am on vacation and I don't have to think about work obligations, but when I am on a normal (non-outdoor) type of vacation, I don't get the same feeling at all. I think it has more to do with the outdoor environment and physical activity.
I recently met someone who works as a park ranger, and I became envious of her job. I would love to patrol the woods all day as a ranger, or to be a mail carrier walking from house to house. I make much more money as a programmer, but "money cannot buy happiness", and I wonder often if I should change course.