Flickr user ChicagoEye, who takes excellent photos by the way, writes:
I've been meaning to get in here for years to photograph. This, gang, is the Alfred Caldwell Lily Pond, designed by and named for the Chicago Prairie School landscape architect. Caldwell was a genius and was also responsible for Promintory Point, Montrose Point and, I think, Riis Park on the Northwest Side. Little known fact: Caldwell did the garden atop the podium of Lake Point Tower which is a fantastic piece of work
More details on the pond at the Chicago Landmarks page
