At the top of the nation's second-tallest building, the Willis Tower in Chicago, sightseers standing on glass suspended 1,353 feet over streets shouldn't be alarmed if they hear cracking.
That was the message from Willis Tower officials after some visitors said they heard cracking Wednesday night.
"I had my palms on the floor, and I could feel it cracking," visitor Alejandro Garibay, 23, of Stockton, Calif., told the Chicago Tribune, explaining that he was leaning down for a picture pose. "Honestly, I was in shock, in disbelief. I was scared."
"One of the craziest feelings I had in my life," added his cousin Antonio Saldana. "I thought I was going to fall through."
The pane of glass on the 103rd-floor area known as the Ledge is coated to prevent scratches, officials told the Tribune. When someone scratches the glass, it's normal for the coating to crack.
"It did what it was designed to do," Willis Tower spokesman Bill Utter told the paper.
The Ledge was immediately closed to restore the coating, but was expected to open later Thursday.