Millennium Park: This 24.5-acre space is used to showcase cutting-edge art, architecture and landscaping; it also acts as a backdrop for concerts and festivals. Most visitors come to Millennium Park to see the Crown Fountain and Cloud Gate, better known as "The Bean".
Grant Park & Buckingham Fountain: Often referred to as "Chicago's front yard," Grant Park is a large swath of green space. Here is where you'll find several of Chicago's most popular things to do, including the Field Museum, the Art Institute of Chicago and the Shedd Aquarium.
Willis Tower Skydeck: Occupying the 103rd floor (the second-tallest building in the Western Hemisphere after One World Trade Center), the Skydeck boasts breathtaking views of the city. Visit on a sunny day and you may be able to see far beyond Chicago's borders to other parts of Illinois, as well as to Indiana, Michigan and Wisconsin.
The Shedd Aquarium: Is home to more than 650 species of fish, reptiles, amphibians, invertebrates, birds and mammals from across the globe
Source: http://travel.usnews.com/Chicago_IL/Things_To_Do/