From the Sears Tower website:
The Ledge brings an exhilarating new experience to the Skydeck. At 1,353 feet up, The Ledge’s glass boxes extend out 4.3 feet from the skyscraper’s Skydeck on the 103rd floor, providing never-before-seen views of the city. An unmatched view is not all the Skydeck offers. From the moment visitors arrive they enjoy interactive and educational attractions that not only highlight the iconic landmark, but also celebrate Chicago’s sports, architecture, pop-culture, history, food, music and people.