Good morning. I'm Steve Inskeep with a tale of the Willis Tower, the Chicago Skyscraper formally known as Sears. There's a glass box on the side where you step out standing on a glass ledge 103 floors up. Some tourists asked if it could break. The guide said, no, it was unbreakable. So they stepped out, and that's when they heard the cracking. An official insists it was just a protective coating that shattered beneath their feet. Workers edged out to repair it. It's MORNING EDITION. Transcript provided by NPR, Copyright NPR.