The Sears Towers in Chicago opened its newly added glass balconies to public on 02 Jul 09. The visitors get a panaromic view of the city and an unobstructed view down from 412 meters up. The walls, floor and ceiling are made of 3.8cm thick glass and jut out 4 feet from the 103rd floor. Affectionately nicknamed "The Ledge", these protrusions can hold upto 5 tons of weight. These are designed to retract when the windows get washed.

http://news.yahoo.com/nphotos/Sears-Tower-unveils-glass-balconies-Skydeck/ss/events/tr/070109searstower103

http://www.examiner.com/x-1406-Chicago-Community-Life-Examiner~y2009m7d2-Chicago-Sears-Tower-unveils-The-Ledge

http://crickler.com/crickler.html

http://www.mirror.co.uk/news/top-stories/2009/07/02/amazing-pictures-of-new-sears-tower-balconies-1-353ft-high-115875-21488996/