The US Steel Tower in Pittsburgh.
This is the tallest building in downtown Pittsburgh and one of the 50 tallest in the world at 64 stories. It is a monument to Pittsburgh’s history as it used to be the headquarters of USX Steel, which was the conglomerate that was created when JP Morgan bought Carnegie Steel.
What people don’t know is the building has the largest flat surface of any major skyscraper in the world at about an acre. There have been some movements to turn it into a park but the owners of the building – according to wikipedia – have never replied to requests by local organizations. I used to work in a long closed restaurant that was at the top of the building and it’s possible to see clouds roll by your window.