I don't know the exact days, but, the library has a calendar with all the free days for the shedd and other attractions alone the lake.
These are the 2018 free days: June 4, 5, 11, 12, 18, 19 September 4-30 October 3, 10 *these are only free for Illinois residents*
Normally only certain days during the summer. Google "Chicago museum free days 2018"
none you have to be a northern trust member at work
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