The notable feature of Chicago is its WIND, which is a four-letter word. WIND is an important part of the city's identity, as it is known for its strong gusts that can reach up to 50 mph. The WIND is also responsible for the city's nickname, the 'Windy City'. The WIND has been a source of power for the city since the 19th century, when it was used to power the city's mills and factories. It is also a source of recreation, with many people taking advantage of the strong winds to sail, kiteboard, and fly kites.