"Great, but packed with tourists"
Columbus Drive is really great, and if you're a tourist, it's a must-visit. On the downside, it's a must-visit for tourists. Columbus runs north / south just a block or two west of Lake Michigan, and it's lined with interesting attractions. Millennium Park has the ever-popular Bean (which you really can't leave Chicago without seeing) and rotating visiting exhibits. Farther south, Grant Park has Buckingham Fountain (a la Married with Children), and lots of very pretty parks and gardens.