We also coincidentally stumbled upon a Buick commercial being filmed - see photo below - and ended up crossing this bridge (on w. monroe st) ignorantly while they waited to resume filming. I thought it seemed strange that the other "pedestrians" on the bridge were dressed so nicely and had cute shopping bags. It made me suddenly very aware of my tangled, wind blown hair and scruffy Gap slip-ons I've worn all summer.
(We also spent some time in Millennium park and had sandwiches from the Corner Bakery. I love the open grassy area by the outdoor theater. And, Chicago in general.)