Let's face it, one of the eerie appeals to "The Ledge" is of the rollercoaster variety: the thrill of feeling like you're in danger even while you're not.
But really, could that glass break?
"The boxes, which opened last week as part of an extensive renovation of the tower's observation deck, are among the most recent, and more outlandish, projects that use glass as load-bearing elements," the New York Timesreports in its ScienceTimes section. "But all glass structures have at least a bit of daring about them, as if they are giving a defiant answer to the question: You can't do that with glass, can you?
"You can. Engineers, architects and fabricators, aided by materials scientists and software designers, are building soaring facades, arching canopies and delicate cubes, footbridges and staircases, almost entirely of glass. They’re laminating glass with polymers to make beams and other components stronger and safer - each of the Sears Tower sheets is a five-layer sandwich - and analyzing every square inch of a design to make sure the stresses are within precise limits."
In other words, the thrill is real, but the danger is not.
"Each glass box is comprised of three layers of glass laminated into one seamless unit," according to the USGlass News Network. "The low-iron, clear glass is fully tempered and heat-soaked for durability. The glass panels weigh 1,500 pounds."
Because that scintilla of doubt is part of the experience.