As well as going to and from school, I would have passed the building regularly going into town as it was one of the available routes.
For the past nine years, I have passed nearly every day – at least once a day.
Yet it was only last November that I spotted this lovely detail.
It appears to be quite simple. Most things are when you know what you are doing. A symmetrical cut at the external corner of a stone provides a revelation – a lovely butterfly, even if it took me forty years to spot it.