Conventional city wisdom will have you avoid all touristy areas at all times, and while there's something to be said for not paying $22 to wait in line for three hours at the Sears Tower, sometimes it's fun to play tourist whether you are one or not.
First of all, get drinks at the Signature Room—The Willis Skydeck is lame, but the Hancock Tower has a bar/restaurant at the top that you don't have to pay or wait in line to visit. The drinks are expensive and the bar food isn't great (brunch is another story), but the women's bathroom has the best, most Insta-friendly view in the city. Snap a shot and watch the likes roll in.
Then, pick a museum, any museum. If you think museums are boring, you are either six years old or in dire need of a cultural education. Guess what? You can find just that at the many museums around the city, most of which have free days. Joy to the world.
The Art Institute is great for a #meaningful date and the cafe is delicious. Take lunch outside into the courtyard on a sunny day and pretend you're vacationing in Europe. The Shedd Aquarium is fun if you're stoned or accompanied by little children (or both), and the Museum of Science and Industry is worth a trip down to Hyde Park because they have a giant mirror maze!
Hang out in Millennium Park. In the summer, there are free concerts, movie nights, and yoga pop-ups every day of the week. Bring a blanket and a cheese platter, or do some weird drugs and lie on the grass, lost in the splendor of outdoor music. In the winter there's a free ice rink in the shadow of the Bean, which is, incidentally, the best place in the city for a skinny selfie.
Go to the beach! There are so many beaches. You should get well-acquainted with them all. North Avenue beach is always a shitshow of teenbros, illegal drinking, and impromptu volleyball. Montrose is a less-crowded party beach with a slightly older crowd. Oak Street is small but packed with coolers and both male and female Viagra Triangle regulars—lots of fake boobs and spray tans. Fullerton has a more laid back family/college vibe. 57th Street is peaceful, scenic, and clean. So is Foster. The list goes on. Find your favorite beach and throw down your beach blanket. Don't forget the sunscreen or the whiskey flask disguised as sunscreen.
Also, bike along LSD or the 606. Both are easy, scenic routes, and biking is good for you, dammit.
Crawl through some art. The Flatiron building in Wicker Park has an art crawl on the first Friday of every month, and a lot of the artists in the building give out free wine and beer to encourage drunken purchases, and while free alcohol is always cool, free art shows are even cooler. If you need a similar event for the second Friday of every month, check out the Second Fridays Gallery Night in Pilsen.