The tallest building in the United States, the Willis Tower in Chicago, Illinois, stands 1, 450 feet high.

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'A few months ago, some scenes for the new Transformers movie were filmed here, ' says Dave Lacki, a Willis Tower guide.

BBC: Chicago��s celluloid city

In an unrelated story, 31-year-old Zac Vawter, who lost his leg in a motorcycle accident, climbed 103 floors of Chicago's Willis Tower wearing a bionic leg.

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Of the top 10 tallest buildings in the world right now, the only U.S. property is the Willis Tower (Sears Tower) in Chicago standing at 1, 451 feet.

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The tower's builders say it will surpass Chicago's Willis Tower as the tallest building in the United States, with a final height of 1, 776 feet -- a nod to the year of the Declaration of Independence.

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If it didn't have the spire, One World Trade Center would be shorter than the Willis Tower in Chicago, which stands at 1, 451 feet and currently has the title of tallest building in the U.S., not including its own antennas.

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

BBC: Chicago��s celluloid city