There are all kinds of options from Chicago. You might look at a trip around the lakes and back across Michigan. In the past few years I have had some really good trips using Amtrak to a point and riding back or vice versa. They have made it progressively easier to travel with a bike on their trains. You could ride up to the twin cities and down the Great River Road as far as time allows. There are lots of interesting ideas in the midwest.
Look through the trips on my blog and see if you get some ideas.
Marc