I took this picture last December at the Art Institute while I was in Chicago visiting my sister and her family. Somehow, I didn't write down exactly what it was (or photograph the description tag, which is usually what I do in such a situation).
It's definitely Sullivan, and I'm pretty sure it's part of the elevator grillwork from the Chicago Stock Exchange. Although, now that I'm thinking about it and writing this up, I think it could also be an air grille from that or another building.
It's fun to bring images like this into CAD or some vector-based drawing program and analyze them in terms of their fundamental geometry of lines, circles, and arcs. Hey, that gives me an idea for another whole post!
But now I have to go teach, so that's for another day. Cheers!