Millennium Park garage is cheaper to all day and this park is there.
South Columbus drive has public parking. Make sure to feed the meter. or there is millennium Park garage entrance going north on south Columbus drive towards Randolph street . As soon as your in the lower garage make a right n follow the signs toward the stairs wich will let you park closer to the park. Take the stairs to go up and you will come to the main level just head out and you eill be by the rock climbing exit.
Under the park. Grant park garage
Take transit, parking is over $30 in that area.
What everyone else has said***
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