What is the Willis Tower in Chicago and why is it significant?

The Willis Tower, located in Chicago, Illinois, is a skyscraper that stands at 1,450 feet tall. It was the tallest building in the world for nearly 25 years and held the title of tallest building in the Western Hemisphere for over 40 years.

The tower was designed by Skidmore, Owings & Merrill and was completed in 1973. It was originally known as the Sears Tower until 2009, when it was renamed the Willis Tower after the Willis Group Holdings, a London-based insurance broker.

The Willis Tower is significant not only for its height and architecture, but also for its impact on Chicago's economy and culture. The tower is home to offices for many large corporations and has served as a symbol of the city's economic and architectural strength. It is also a popular tourist destination, attracting millions of visitors each year to its Skydeck observation deck, which offers stunning views of the city and surrounding areas.