Jackson Park was designed by legendary landscape architect Frederick Law Olmsted in 1871. It was the main site for the 1893 Columbian Exhibition, but little evidence remains as all the buildings have been demolished since. Jackson Park was originally supposed to be part of a grand South Park, encompassing both it and Washington Park, connected by a canal running through the Midway Plaisance.
The Osaka Garden is the only remnant from the Columbian Exhibition. It is named for the city of Osaka, which donated funds to restore the Japanese garden after it had been vandalized during World War II. Other highlights include the Golden Lady, a gilded replica of Daniel Chester French's The Republic. There are nature trails, which are great for bird watching and two different beaches.
Jackson Park covers 500 acres on the South Side. If you're around Hyde Park and the University of Chicago, stop by for some unwinding.
Train: 55th-56th-57th Street (Metra), 59th Street (Metra)