The Shedd Aquarium is one of the greatest aquariums I have ever visited. The building is magnificent - a true temple to the natural world. There are two admittance rates: one that allows access to just the fish and one that allows access to more. If you're short on time, the fish will keep you plenty busy, but to see everything is quite worth it. Go very early to miss the lines - they can be quite long during the day. If you're going many places, it's worth looking into the Chicago Pass - this is on it. The Shedd does offer a student ID rate.