Check out the website Openhousechicago.org. To be held in mid October and sponsored by the Chicago Architecture Foundation. You will be able to visit over 150 places in Chicago that are generally not opened to the public. For details download their event guide.

I have volunteered for this event for the past 3 years and will porbalby do it again this year.

Here is my Flickr album from the 2014 event.

https://www.flickr.com/photos/k9jdk/sets/72157648439114028/

I've been in a lot of places I didn't know existed thanks to OHC! It's well worth it.