Millennium Park's Jay Pritzgar Pavillion is a behemoth, awe-inspiring theatre. 4 to 5 thousand seats, not including the lawn.
I attended several free concerts last summer and sat near the seats and on the lawn. One of my dreams would come true if I could see Kristin Chenoweth perform a concert on a beautiful summer evening at the Pritzgar.
Millennium Park is much more than the Pavillion. Gardens, unusual fountains, ground breaking art work, ice rink/restaurant and the Harris (indoor) Theatre, dot the grounds of the park.
Check it out if you can or at least take a virtual tour. It is situated right on the water front and right next door to the the Art Institute.
" ...the happiness in the tune convinces me that I'm not afraid."