I have been in Chicago Union Station a number of times during layovers between CZ, EB, and LSL - all of a few hours. Every time, I have hung out some in the Great Hall. I usually travel with a guitar, and have sat there and strummed and as a result made many people's acquaintance. It is a beautiful room and I have never understood why more people don't use it. The point has been made that you hear no announcements, which is GOOD thing if you don't expect your train to depart for several hours.
If you have a layover, it is probably the quietest place you can hang out, not as comfy seating as the 1st class lounge but you don't have to put up with the TV being on all the time and all the lounge occupants staring at it like zombies. A huge refuge from the mayhem of the "modern" parts of the station.
Best to you all.