I managed to pull something in my back this morning - so I've been taking it carefully all day. I decided to try swimming this evening to see if gently exercise would help ease it: I'm not sure it helped, but it didn't make things worse either, which is encouraging. And I enjoyed the swim (last one before Christmas).
Afterwards, as I was leaving, I spotted other people leaving the building as well. I rather liked the patterns on the wall created by the overhead lights.