The owners of the Sears Tower, the tallest skyscraper in the United States (Chicago), inaugurated last week four glass box viewing platforms. These balconies are suspended 1,353 feet (412 meters) in the air on the 103rd floor. They are 10ft high and 10ft wide and can hold 5 tons with their 1.5 inch thick glasses.
Really impressive and definitively something to try...