http://metrarail.com/System_map/index.html

I'd consider driving along I-88 to Aurora, then catching the Metra Rail downtown. Then you can cab anywhere, take the double-decker sightseeing buses, whatever. Back to Northwestern Station for the Metra ride back out to Aurora at the end of the day, then home. The drive by car in and out of downtown can be pretty brutal, and parknig is expensive.

Downside is you will be tied to the train schedule - shouldn't be a problem though. During the week, earliest train leaves Aurora ~4:30AM, latest train leaves Chicago for Aurora ~12:40AM. Check link for weekend/holiday schedules.