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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.

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.

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

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

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