Sears Tower

The Willis Tower, known as the Sears Tower until 2009, is the tallest building in the city of Chicago. It stands in the Loop neighborhood at the corner of South Wacker Drive and Adams Street. With a roof height of 442 meters (1,450 feet) and an overall height of 527 meters (1,729 feet) including its antennas, it is not only the tallest structure in the city but also one of the most important skyscrapers in the world. Construction began in 1970 on behalf of the retail giant Sears, and the building opened in 1974. At the time, Sears was the largest retailer in the world, and the tower housed the company's headquarters. The architectural design is unique: the tower consists of nine square tubes arranged in a 3x3 grid, which end at different heights. This stepped structure gives the building an ever-changing appearance from different perspectives. The load-bearing elements are made almost entirely of steel, which still makes the Willis Tower the tallest building of this type today. The facade is clad in black aluminum and includes around 16,100 windows.

The tower's history is closely tied to the evolution of height records in skyscraper construction. Upon its completion, it surpassed the World Trade Center in New York as the tallest skyscraper in the world. Over the years, there were several controversies and changes in the rankings, because measuring height yields different results depending on the definition (overall height, roof height, or highest occupied floor). It lost the title of tallest roof to Taipei 101 but long held the record for greatest overall height, until the Burj Khalifa in Dubai took over all the records in 2010. Today, the Willis Tower is the second-tallest freestanding structure in the United States, after One World Trade Center. The name was changed to Willis Tower in 2009, after the insurance company Willis Group Holdings acquired naming rights and leased office space. Despite the official renaming, the building is still often called the Sears Tower in everyday speech, since that name has been closely tied to the city's history for more than three decades.

For visitors, the tower offers an impressive observation platform in the Skydeck on the 103rd floor, at a height of 412 meters (1,353 feet). On clear days, you can see up to 80 kilometers (50 miles) from here, taking in as many as four different U.S. states. Two of the fastest elevators in the world carry guests to the platform at a speed of about 8 meters (26 feet) per second, in just 45 seconds. A special attraction is the three enclosed glass balconies on the west side of the building. They let visitors stand on a glass floor that is attached to the facade on only one side, so you can look straight down through the floor to the ground far below. Since the collapse of the South Tower of the World Trade Center, this has been the highest observation platform in the U.S. The building's lobby also features the well-known sculpture The Universe by Alexander Calder, which gives the entrance area an artistic touch.

Besides serving as a tourist attraction, the Willis Tower is above all a large office building with roughly 350,000 square meters (3.8 million square feet) of floor space. Its tenants include international companies such as United Airlines, which maintains its operations center here, as well as various insurance companies and law firms. The building's technical infrastructure is designed to cope with this enormous height, with 104 elevators and several underground levels. The total weight of the structure is around 220,000 metric tons. Despite its massive size, the tower deviates minimally from the vertical because of its slightly asymmetrical design and the uneven load on its foundation. The tower remains a central symbol of the Chicago skyline and an example of engineering excellence that is of great importance both historically and architecturally.