This building has been in the news twice recently. The tallest building in the world from 1973 to 1998, and currently the tallest skyscraper in North America, the building formerly known as the Sears Tower was recently renamed for some holding company. Many Chicagoans will forever refer to it by its original and proper name. I don't want to live in the past, so I'll just call it 233 South Wacker Drive.
Less infuriatingly, four glass "skyboxes" which peek four feet outside the walls of the 103rd-floor observation deck were added in January 2009. I had a chance to hear one of the project engineers speak tonight. He began his presentation with a picture of Ferris Bueller and friends with their foreheads pressed up against the windows so they could look straight down. The purpose of adding the skyboxes was to enable users to to get Ferris's view without getting forehead prints on the glass. Now, glass-bottom observation ports on tall structures are nothing new - the CN tower has 'em, for example - but the skyboxes at 233 S. Wacker are unique in that (1) they have no steel in the sight lines, and (2) they are retractable. Amazing! The glass floor is hung from an overhead steel frame by the glass walls alone! And, AND, it was a design requirement that the skyboxes retract to be flush with the rest of the outer walls such that they wouldn't interfere with normal operation of the building's automated window washing equipment.
Here you can see the one of the boxes from another box. All four boxes are on the western wall of the building. The steel tubes from which the box hangs are plainly visible at the top of the box.
The boxes deliver on the promised straight-down Ferris Bueller view, as shown below. Those are my feet there, with nothing but three panes of glass and 103 stories of air between them and Wacker Drive.
Finally, just for fun, a picture of downtown (looking north) and a long-exposure shot of the view to the northwest, including traffic on the Kennedy Expressway.