Nearly six million people have stepped out onto see-through ledges atop Chicago's tallest building to see the streetscape below and the surrounding metropolitan area.
The Willis Tower, formerly known as the Sears Tower, released that figure this week -- four years after the tourist attraction opened in 2009.
The series of glass bays jut out from the 103rd floor of the building that's dominated Chicago's skyline for four decades.
The see-through floors are collectively known as The Ledge and they are in the longer-established Skydeck section of the skyscraper.
More than 1.5 million visitors stepped out onto The Ledge in 2012 alone.