John Hancock Building

875 North Michigan Avenue — still "the Hancock" to anyone who lives here — was completed in 1969 and was, briefly, the tallest building in the world outside New York. Its X-braced exterior is the whole point: the diagonal cross-bracing carries the wind load on the outside of the structure, which is why the tower can taper and stand as lean as it does. It made the engineering visible instead of hiding it, and it changed how tall buildings were built.

Photographed June 2024. In black and white the bracing reads as pure geometry — the dark X's marching up the face, the tower narrowing into the sky. It is one of the few skyscrapers you can identify from a single fragment of its wall.