J.W.
I was JUST there on Monday. If you go on their website under "planning your trip" and discounts (I think), it will tell you the dates that are free to go on. Monday was a free day. It only includes 3 exhibits, but they are pretty big and it took us 3 hours to get through them with 2 2-year olds and a 1 year old. They didn't know what they were missing with the other exhibits that you have to pay for. Friends of ours purchased the tickets to see the dolphin show with their 4 year old girls, and they were very dissapointed in the show. I guess it wasn't worth what they payed for it. Parking is also pretty expensive: $16 for up to 4 hours and $19 after that at Soldier Field parking garage. If you do decide to pay to go to the aquarium, the rates are cheaper than what they state on the website, which was a nice surprise. We had a really great time and I hope you do too. :)