I really like hiking and kayaking because they allow me to be fully immersed in nature while observing and enjoying its grandeur. Both these forms of exercise test your endurance while opening up your senses to the outside world.
I have recently taken up archery as a new form of physical and mental exercise. I usually take my target out into the woods and shoot my arrows. The quiet of the woods juxtaposed against the subtle sounds of a stream and birds allow me to relax my mind. Holding the bow taught as I draw back works my back and arm muscles as i steady my core and control my breathing before letting go of the bowstring and hearing the "thwip" of the arrow meeting it's mark. It is all a wonderful experience.