I read this morning that to live long, I should take 150 minutes of exercise a week and preferably play tennis.   Nearly my only exercise is walking across the park which today, unusually, I have done three times, once early when there was still ice on the lake, and a second time later when there was a flash of red in the distance which was the changing of the guard:-

I had also never noticed the keystones on the houses in Queen Anne’s Gate:-