Looks like this is being added, but after August ~maybe a return trip?
http://abc7chicago.com/society/art-on-themart-to-bring-art-to-riverwalk-/3139849/
http://abc7chicago.com/society/art-on-themart-to-bring-art-to-riverwalk-/3139849/
If you're willing to go to the suburbs, the Morton Arboretum and Cantigny are nice.
http://www.mortonarb.org
https://cantigny.org