Chicago is the birthplace of the Skyscraper. here are some of my favorites.
Sears Tower (Original) / Nichols Tower
906 S Homan Ave, Chicago, IL 60624
http://www.homansquare.org/about/nicholstower/
1-773-265-4404
Sears Tower (Willis)
233 S Wacker Dr, Chicago, IL 60606
Main building Website
https://www.willistower.com/
Skydeck / Ledge
https://theskydeck.com/
1-312-875-9447
Tribune Tower
435 N Michigan Ave, Chicago, IL 60611
1-312-222-3787
Wrigley Building
400-410 N Michigan Ave, Chicago, IL 60611
http://www.thewrigleybuilding.com/
1-312-923-8080