1. Chicago is known as the "Windy City", but the nickname originally referred to its politicians' long-winded speeches, not the weather.
 

2. The city reversed the flow of the Chicago River in 1900, an engineering feat designed to prevent pollution from contaminating Lake Michigan.
 

3. Chicago is the birthplace of the skyscraper—the Home Insurance Building (built in 1885) was the world’s first building to use a steel-frame structure.
 

4. The city’s deep-dish pizza, created in the 1940s, is a world-famous dish with a thick crust, layers of cheese, and chunky tomato sauce on top.
 

5. The first-ever controlled nuclear reaction took place in Chicago in 1942 under the leadership of physicist Enrico Fermi, marking a key milestone in atomic energy development.