Any must-see sites in Chicago?

My best friend and I are both single, college grads in our mid- twenties and we are planning a trip to Chicago this June. We will be in the city four five days, and our hotel is in a prime location overlooking the Navy Pier. I've gotten a few tips from friends of some things we must do, like a Cubs game at Wrigley Field, Millenium Park, Navy Pier, and a variety of other big tourist attractions. But, I am in seek of some cool restaurants, lounges, bars, etc that are more off the beaten trail, but still offer a local vibe with cool people. Any Suggestions? Thanks so much!