Aon Center
When it opened in 1973 as "Big Stan," this 83-floor tower was the fourth-tallest building on Earth — and clad entirely in marble.
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Built as Standard Oil of Indiana's showpiece headquarters, it briefly held the title of Chicago's tallest before the Sears Tower overtook it in 1974. The engineering is the story: a tubular steel frame with V-shaped perimeter columns designed to resist earthquakes and cut sway, rising 1,136 feet in the Northeast Loop. It once also held the title of tallest marble-clad building in the world.
What to look for
- V-shaped perimeter columns at the base — part of the earthquake-resistant tubular steel structural system
- The building's mass against the skyline: at 83 floors it is Chicago's fourth-tallest, behind Willis Tower, Trump Tower, and St. Regis
- The address: 200 East Randolph, once world headquarters of Amoco before its merger into BP
A working office tower in the Northeast Loop; no public observation deck — best appreciated from Millennium Park or the Riverwalk for full height context.
Aon Center is one of 37 sights worth the detour in Chicago, all bundled offline in Voyage GO — download the Chicago pack and it sits on your map with no signal, filling your travel passport the moment you walk past.
More to see in Chicago
- Willis TowerIt held the world's tallest title for nearly 25 years after opening in 1973 — and the Skydeck is still the highest observation deck in the United States.
- Art Institute of ChicagoFour paintings you've seen your whole life — Nighthawks, La Grande Jatte, The Old Guitarist, American Gothic — hang in the same building.
- John Hancock Center (875 N Michigan Ave)A moving platform pivots you 30 degrees outward over the Magnificent Mile — 1,128 feet of nothing beneath your feet.
- United CenterThe Bulls hardwood floor is literally assembled over the Blackhawks ice and taken apart game by game — two teams, one frozen surface, shared by puzzle.
- Soldier FieldThe NFL's oldest stadium lost its National Historic Landmark status because of the renovation meant to save it.
- Home Insurance Building SiteChicago halted construction mid-job — city officials had never seen a steel skeleton carry a building instead of its own walls and stopped work to investigate its safety.