On the north side of the Chicago River, at 400 N. Michigan, is the striking Wrigley Building. Built by Wm. Wrigley Jr. the as headquarters of his gum company,
the 30-story South tower was completed in 1921. The clocks are 19.5 feet in diameter, and are on all four sides of the tower. The North tower, at 21-stories,
was completed in 1924. Marking the beginning of the Miracle Mile of North Michigan Avenue, it was the first office building to have air conditioning.
The towers are clad in glazed terra-cotta and are occasionally hand-washed.