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?"'