Willis Tower contains Chicago’s famous glass viewing balconies called The Ledge.
The Ledge consists of glass boxes projecting from the Skydeck on the tower’s 103rd floor. Visitors can step onto the transparent floor and look down toward the streets below. The Skydeck is approximately 412 metres above ground, although the tower’s roof and antenna reach higher.
Willis Tower was completed in 1973 and was designed by Skidmore, Owings & Merrill. Its bundled-tube structural system helped make the 442-metre building possible while creating the familiar stepped silhouette of nine connected square tubes.
The building was originally called Sears Tower and was renamed Willis Tower in 2009 after a new naming-rights agreement. Many people still use the original name. The Ledge is a visitor attraction inside the building, not a separate tower or an external elevator platform.