The tower and rotating platform opened in June, ahead of the Olympics.

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"It's a pretty awesome feeling, " Juan Estevez said from a temporary platform on the roof of the tower where he and other workers watched the milestone.

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The complex is topped by a 340m-long SkyPark with a capacity of 3, 900 people and a 150m infinity swimming pool, set on top of the world's largest public cantilevered platform, which overhangs the north tower by 67m.

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The nesting platform is about half way down the tower and the falcons regularly take local, wild birds for food.

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Up at the viewing platform of the Willis (formerly Sears) Tower, the staff are used to movie stars wandering around.

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The Cupola is an observation tower that will be used to control robots working on the exterior of the platform.

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