Navy Pier - take the boat tour to Lake Michigan. Best skyline photo op of Chicago is 1 mile into the lake.
Chicago River - take the kayak tour or the architecture boat tour.
Lake Shore - rent a bike and bike from Lincoln Park Zoo to Navy Pier to the Museum Campus to even Hyde Park promotory point. Its all flat terrain so if you are healthy or used to worse terrain, it would be an easy route.
Sears Tower - just do it. Its good if you are a tourist. Dont listen to locals when it comes to this building.
Interesting Food Experience:
The Wierner’s Circle at 2am. They sell hotdogs to people coming out of bars. Order the chocolate shake if you are brave; prepare to be berated. It’s a weird experience for sure but its a story worth bringing back home with you.