Do most places go to this kind of trouble for sidewalk grates? This thing is above and--
--below and beyond.
To me, a superfluous detail is something beautiful that doesn't have to be--something that enhances the look of a functional item, just for the sake of art. This grate reminds me of Celtic art in its interconnectedness. It is medieval, serious, dark. It's artwork I can hear (the clash of metal against metal) in my imagination.
It's a delight to walk around the Caltech campus and admire the superfluous details. Be sure to look up as well as down.