If You Have 1 Day
If you have only a day in Chicago, sample some of the city's most distinctive areas. Assuming that you'll be visiting during nice weather, start the day in the Loop, either on a self-guided tour or one organized by the Chicago Architecture Foundation (the early-skyscraper tour is a good primer). Thanks to the Great Fire of 1871 and the determination to rebuild, Chicago has been a world leader in architecture for more than a century. If you're a shopper, spend the afternoon scoping out Michigan Avenue or strolling among the boutiques on Armitage Avenue. Or, if you're here in the summer, take the El uptown (along with a whole lot of business types taking a "long lunch") and spend the afternoon watching a Cubs game at historic Wrigley Field. If the weather's lousy, head indoors to one of the city's great museums, such as the Art Institute, the Field Museum of Natural History, the Shedd Aquarium, or the Adler Planetarium. To top off the day, catch a play at one of the city's top theaters: Goodman, Chicago Shakespeare, or Steppenwolf.
If You Have 2 Days
Spend the first day in the downtown area. Walk around the Loop (as mentioned above) to see the buildings and the city's extensive sculpture collection. If it's a Saturday, get free tickets at the Chicago Cultural Center for the Loop Tour Train, which offers a guided overview of the city from the century-old elevated train (on any other day of the week, you can hop the El yourself for the same views, without the commentary). Next, visit one or two of the city's premier museums. Finish off the day with a shopping trip up the Magnificent Mile (and maybe a trip to the top of the Hancock Building) or a gallery-hopping expedition in River North. Both areas have plenty of excellent restaurants for dinner. If you've still got the energy, take an evening stroll along Navy Pier and a spin on the Ferris wheel. Then pick a boat along the dock for a nighttime cruise and view the shimmering skyline from the lake.
On the second day, head for a neighborhood on the North Side, such as the Gold Coast, Lincoln Park, or Wicker Park, and explore. In the afternoon, you won't be far from Wrigley Field, where you can see the Cubs play. In the evening, dine at one of the many ethnic restaurants along Clark Street or Southport Avenue. Spend the rest of the evening at one of the big-name theaters or perhaps at a more offbeat show in the Wrigleyville area.
If You Have 3 Days
Begin the third day with a trip to Hyde Park, where you can see the University of Chicago and Frank Lloyd Wright's Robie House, among other sights. Then spend a few hours at the fascinating Museum of Science and Industry. If you have time left, you could head back north and visit another museum. One worthy candidate is the Mexican Fine Arts Center Museum in Pilsen, a vibrant Hispanic community south of the Loop that has wonderful outdoor murals and some charming bakeries along 18th Street. If it's a nice day, however, walk up North Michigan Avenue or cross over to Oak Street Beach for a stroll (or roll, with a rented bike or blades) along the lake up to Fullerton Avenue, where you can wander around the zoo and the conservatory, or the Peggy Notebaert Nature Museum. If you have an extra couple of hours of daylight, jump in a cab and head for nearby Armitage Avenue, lined with some of Chicago's most unique boutiques and retail shops. Choose one of the neighborhood's many good restaurants for dinner and then one of its jazz or blues clubs for a finale.