Walking is good for your health whether it is accomplished on an expensive treadmill with various speeds and levels of difficulty, or on a brisk trip down a tree-lined dirt lane. I choose the latter because I require the prospect of the unexpected.
On a treadmill, you can trot away in the same location to your favorite tunes, or watch TV and hope your feet don't get confused and launch you backwards.
On a real walk you can see this:
and sometimes this:
Sounds of birds, frogs and neighborhood dogs punctuate the stream of thoughts that wash through consciousness once immersed in nature. It's impossible not to have thoughts. Today on my walk, I thought about how much I love living things; about the inconsequence of a single life; about the contradiction of death to the proposition of life. And then I realized that one's own death is an imperceivable state, a sudden midnight with no new dawn, and our bit of time ends but remains part of all of time. Try that on a treadmill...and then take a real walk.