One of the largest parks in Chicago and the host of many annual events, such as Lollapalooza, Taste of Chicago, and Blues Fest.  It has also hosted two NFL Drafts.  A lot of amazing sites in the park, such as Buckingham Fountain.  Many of the sites in the park have their own galleries. 

Learn more from Wikipedia.

See galleries of the sites in Grant Park:

Agora
Buckingham Fountain
John Alexander Logan Monument
Paris Metro Entry
The Bowman and the Spearman