If you're scared of heights, it may be time to look away now.

Not content with having the tallest building in America, the owners of Sears Tower in Chicago have installed four glass box viewing platforms which stick out of the building 103 floors up.



The balconies are suspended 1,353 feet in the air and jut out four feet from the building's Skydeck.



Floating on air: Visitors get their first view from The Ledge, four glass balconies suspended from the 103rd floor of Chicago's Sears Tower

Designers say the platforms - collectively dubbed The Ledge - have been purposely designed to make visitors feel as they are floating above the city.

The reward is 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.

'It's like walking on ice,' visitor Margaret Kemp, from Bishop, California said. 'The first step you take you think "Am I going down?"'

Fearless: Anna Kane, five, spreads out on the floor of the 10ft square box which is 1,353ft up

Spectacular: She also enjoyed amazing views out across the city

'At first I was kind of afraid but I got used to it,' 10-year-old Adam Kane from Alton, Illinois, said as clouds drifted by below.

'Look at all those tiny things that are usually huge.'

John Huston, one of the owners of the Sears Tower, even admitted to getting 'a little queasy' the first time he ventured out on to the balcony. However, after 30 or 40 trips, he seems to have got used to it.

Thrillseekers: The boxes jut out four feet from the building and were specifically designed to make visitors feel as if they are floating

'The Sears Tower has always been about superlatives - tallest, largest, most iconic,' he said.

'The Ledge is the world's most awesome view, the world's most precipitous view, the view with the most wow in the world.'

The balconies are 10ft high and 10ft wide, can hold five tons, and have glass which is 1.5 inch thick.

Unfazed: Although some adults felt dizzy after experiencing the Ledge, children seemed to take it in their stride

Long way up: Even the floor of the platforms are glass - few were brave enough to look straight down

Inspiration 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.

Architect Ross Wimer said: 'We did studies that showed a four-foot-deep (1.2 metres) enclosure makes you feel like you're floating since there's only room for one row of people, not two.'

The Skydeck attracts 25,000 visitors on clear days. They each pay $15 to take an elevator ride up to the 103rd floor of the 110-story office building that opened in 1973.

The viewing platform is on the 103rd floor... towering above the height of buildings such as London's Canary Wharf Tower