I grew up surrounded by concrete, broken glass and white dog shit. I wasn't allowed out, but indoors was even worse, locked in and kept prisoner in yet more filth and with added danger from a raging arsehole. I wanted to get away, but I wasn't allowed to. I spent a lot of time staring at the sky out the window until I was caught looking outside and punished for it.
I have no real desire to walk through shuttered up shops, overfilled litter bins and avoiding street beggars and pissheads sitting on the benches in the town centre. However, it's quicker to walk through that than wait in it for a bus or sit on a bus doing the equivalent of a 940 degree turn to get around the completely unused road system that has been closed to sit empty in the hope that somebody on a bicycle might someday choose to use it.
But if there's fresh air, a clear breeze, maybe rain, maybe sunshine, greenery, wildlife that isn't a rat or one legged pigeon and sky instead of yet more grey concrete, mostly deserted office blocks, I feel great. I want to run and walk and sit to catch my breath in a glowing pool of sunlight before continuing onto the second half.
Any exercise is good. The feeling in well worked muscles, of a heart working hard, overrides chronic pain. It's pain that has a purpose, you feel it leave. But add that into a feeling of peace, the lack of mental tension, the way your eyes can relax looking upon an expanse of green rather than the noise and sights of city life, the sight of the sky - it's great and if I can't run, I will walk. And feel alive.