CHICAGO - Visitors to the Sears Tower's new glass balconies all seem to agree: The first step is the hardest.

The balconies are suspended 1,353 feet in the air and jut out four feet from the building's 103rd floor Skydeck. Their transparent walls, floor and ceiling leave visitors with the impression they're floating over the city.

"It's like walking on ice," said Margaret Kemp, of Bishop, Calif., who said her heart was still pounding even after stepping away from the balcony. "That first step you take - 'am I going down?'"

Kemp was among the visitors who got a sneak preview of the balconies Wednesday. "The Ledge," as the balconies have been nicknamed, open to the public Thursday. Visitors are treated to unobstructed views of Chicago from the building's west side and a heart-stopping vista of the street and Chicago River below - for those brave enough to look straight down.

John Huston, one of the property owners of the Sears Tower, even admitted to getting "a little queasy" the first time he ventured out. But 30 or 40 trips later, he's got the hang of it.

"The Sears Tower has always been about superlatives - tallest, largest, most iconic," he said. "Today is also about superlatives. Today, we present you with 'the Ledge,' the world's most awesome view, the world's most precipitous view, the view with the most wow in the world."

The balconies can hold five tons, and the glass is an inch-and-a-half thick, officials said. Sears Tower officials have said the inspiration for the balconies came from the hundreds of forehead prints visitors left behind on Skydeck windows every week. Now, staff will have a new glass surface to clean: floors.

"It's very scary, but at the same time it's very cool," said Chanti Lawrence of Atlanta, adding that she's made her first step toward overcoming her fear of heights.

Adam Kane, 10, of Alton, Ill., rushed to the ledge with his friends and siblings, and they each eagerly pressed their faces to the glass bottom.

"Look at all those tiny things that are usually huge," Adam said.

The balconies are just one of the big changes coming to the Sears Tower. The building's name will change to Willis Tower later this summer. Last week, officials announced a 5-year, $350 million green renovation complete with wind turbines, roof gardens and solar panels.

With the ledge, visitors like Kemp said the nation's tallest building has succeeded in creating something they've never seen before.

"I had to live 70 years for a thrill like this," she said.