From The Washington Post:
Don't look down. Or do, since that's the idea. But brace for vertigo. In the city of big shoulders, this is like standing on an eyelash. It's a glass ledge, 1 1/2 inches thick and poking out about four feet from the 103rd floor of the Sears Tower. There is no frame under the floor, only air — 1,353 feet of it, straight down to the miniature taxis on Wacker Drive. Picture Wile E. Coyote racing off the cliff. Think of the moment when he suddenly looks down. Only you don't actually fall. The reason is an intriguing feat of engineering, a team of designers and builders said Wednesday, swearing on a stack of liability policies as they unveiled the project. The ledge — actually four identical glass boxes suspended near the top of the nation's tallest building — opens to the intrepid Thursday.
The natural instinct is to inch out onto the glass very, very slowly, said sheet metal worker Leo Thier, who took a break from another job to venture into the box. Still in his hard hat and construction boots, he delivered his verdict: “It's fantastic. It's insane.”