Tourists in Chicago are petrified after part of Willis Tower's "Ledge," a glass cube which juts out from the 103rd floor Skydeck, began to crack as they stood on it. (Reuters)

Way, way above the streets of Chicago — 103 floors up, to be precise — sits the Sears Willis Tower’s Skydeck, a tourist attraction that draws more than 1.5 million visitors each year. Inside this room, there are enclosures called the Ledge, a series of glass boxes that let visitors amble out  onto a small, clear floor and look down at the city below. “An unmatched view” is what the Skydeck promises you.

On Wednesday night, some visitors went out onto the Ledge and said they heard it cracking:

One of the people who went out into the box — 1,353 feet above the ground — told NBC Chicago, which first reported the news, that it was a “crazy feeling and experience.”

The cracking was on the protective coating covering all of the Ledge’s glass surfaces, rather than the glass itself, a spokesman for Willis Tower told The Post.

“This coating does not affect the structural integrity of The Ledge in any way,” Brian Rehme said in an email. “Occasionally, the coating will crack, as it is designed to in order to protect the surface of the glass.”

The coating is being replaced, Rehme said. While the Skydeck will remain open during these fixes, the four Ledge enclosures have been closed.

The ledges, which opened in 2009, are made up of three sheets of glass and an invisible layer of resin all bolted to a steel frame at the top of the box. When the ledges opened, the construction chief described how even if all three layers were shattered, the floor would hold. “There’s no problem with putting 5,000 or 10,000 pounds without anything happening,” he told The Post. “It’s been tested.”