And the fact that Chicago being as windy as it is makes it even more impressive.
On windy days, it is possible to see the building "bend", as they are designed to flex under severe weather conditions.
You can even see the curve of the earth from the top floor on a very clear day.
Yeah, looking at the earth curve is cool, I used to fly in small planes just for fun, like hop across the sound for lunch or coffee alot and it was breathtaking on clear days looking at the earth from a small cockpit.