I grew up in Chicago suburbs and very familiar with the city. Great town, but crazy-cold in the winter. Walk through Millenium Park and Art Institute. Visit the Adler Planetarium, the Shedd Aquarium, and the Field Museum. As many have mentioned Deep Dish Pizza is a must and I grew up on Lou Malnatis. MCA (modern art) is good. A touristy, but still fun thing to do is go to the 96th floor of the John Hancock Building, the Signature room (bar), and get an overpriced drink...the views are amazing. Plenty of good breakfast, including a (chain restaurant) called "Yolk". Plenty of good cocktail bars and high-end bars, but don't by-pass all the good dive-bars: Zakopanes, Old Town Ale House, Bialystok. The
Green Mill is worth a trip up to the North Side; used to be a regular hangout past 3am. Most of the Blues Bars in the Loop kinda suck in my opinion. The Original Billy goat on Lower Wacker is till decent. Plenty of good free museums, including the Mexican Museum of Art, museum of contemporary photography. Blackhawks! Make sure to sample Chicago's cultural icon, a fine (crappy) beer called Old Style!