Fodor's Expert Review Aon Center
The Loop
Notable Building
Free
With the open space of Millennium Park at its doorstep, the Aon Center really stands out. Originally built as the Standard Oil Building, the 83-story skyscraper (first referred to as Big Stan) has changed names and appearances twice. Not long after the building went up in 1972, its marble cladding came crashing down, and the whole thing was resheathed in granite. Plans to add an observation deck on the 82nd and 83rd floors have met with delays, and likely won't be completed until 2024.
