alt Hacker NewsStopping and looking at some birds and what they're doing is really relaxing. Be it pigeons, seaguls looking for fries or if lucky a crow or rook.
The corvids looking back wondering what you're doing and they'll communicate back too.
I think becoming a person who would stop and do that, or go birdwatch in general, is probably the important part.
Mean sure, but doing just that misses the learning and specific attention part. Going from "bird" to species, learning about morphological, vocal differences is going beyond "being a little more active and interested in your surroundings". It's really engaging every sensory and cognitive system in concert.
That said, collecting plants or beetles is probably equally beneficial. Geocaching comes to mind too.
Although, I wonder if looking up may contribute, given old people tend deform and bend forward with age. Could affect blood or lymphatic circulation.