You're standing on the Michigan Avenue Bridge. Commonly known as the Michigan Avenue Bridge, it was officially renamed the DuSable Bridge in the early 21st century, to honor Jean Baptiste Pointe du Sable who was the first non-native settler in Chicago.Now, take a few moments to look west down the Chicago River and into the city.  The Chicago River has an interesting history. Once a corridor of commercial activity, the river has been transformed into a recreational area with sightseeing boats and kayaks. There are also pedestrian-friendly promenades along the banks, lined with cafés and eateries.Did you know that the The Chicago River is the only river in the world that flows backward ?Up until 1900, the Chicago River flowed directly into Lake Michigan, but so did all of the sewage generated from the city. The Des Plaines River, which is located west of Chicago, flowed into the Illinois River and makes its way into the Mississippi. Chicago’s drinking water came from the lake, near the mouth of the river, that water became polluted and caused outbreaks of waterborne diseases like typhoid.The Sanitary District of Chicago had to come up with a plan to eliminate the city’s sanitation issues. The top solution was to construct a canal that connected the Chicago River and the Des Plaines River. This project made it possible for a regulated amount of water to leave Lake Michigan via the Chicago River and eventually flow into the Illinois River.To reverse the flow of both the Main Stem and the South Branch of the Chicago River, a series of canal locks were used. This project caused the river to empty into the newly finished Chicago Sanitary and Ship Canal.Even into the 1980s, the river was known for being polluted. In the 1990’s, As part of Mayor Richard M. Daley’s beautification efforts, the Chicago River benefitted from extensive cleaning.Now take a look at the series of bridges which link the Downtown Loop to the North Side, the Magnificent Mile. The Michigan Avenue Bridge is essentially the "Main Street Bridge" of Chicago since it carries a busy roadway including as many as 30,000 pedestrians daily and has been decorated to give it the feel of a gateway bridge. It is the most well-known moveable bridge in Chicago, and is one of the few double-deckers in the city.The moveable bridges, which open to let boat traffic up and down the river, represent engineering marvels.  Chicago has 38 of them, with the first constructed at the beginning of the 19th Century at Dearborn Street.Now look at the huge white building with the clock at the top. This is the Wrigley Building, the first air-conditioned office building. It’s one of the few buildings in the world that needs no other address. Designed by Graham, Anderson, Probst & White, this icon of Chicago’s celebrated Magnificent Mile has welcomed generations of tenants proud to call the Wrigley Building their home.The Wrigley Building offers the best of both worlds. The shops, restaurants, hotels and attractions of the renowned Magnificent Mile are right outside the doors, and just steps away, the government, legal, high-tech, financial, and business centers of this world-class city await. A multimillion-dollar renovation has transformed this landmark building into a state-of-the-art business environment with an exciting new retail component. Discover what’s in store for this acclaimed Chicago landmark.And just behind, on the right, you will see the Tribune Tower. Inspired by the Button Tower of the cathedral at Rouen, France, the Tribune Tower exemplifies the way American architects have elevated office buildings to sacred status. Newspaper publisher Colonel Robert R. McCormick held an international competition to design, "the most beautiful and eye-catching office building in the world,” and in many ways, it succeeded. The tower has all of the traditional elements of a skyscraper plus heritage expressed in flying buttresses, spires, grotesques and more. The base of the Tribune Tower contains 120 stones from important locations all around the world.Photo Michigan Avenue Bridge by vxla is licensed under CC BY 2.0