For this time of the year, I never see a use for renting a car in Chicago for Chicago area use unless wanting to shop outside the city. I really dislike paying for parking in the city, and Chicago has too many crazy drivers on Friday and Saturday evenings. And road traffic to and from the airport can be ridiculously slow at various times while the blue CTA line from the airport to the Loop runs at normal speeds. I have been doing the Blue line for decades, and it’s my main way in and out of the city even though I sometimes Uber/Lyft in and out or drive in. There are the occasional homeless types who are on the Blue line too, but I have never had it be a problem by just doing my own thing.
The best skybar in the city is my relatives’ rooftop bar on top of the house downtown with great views of the skyscrapers, but I am not allowed to have parties there while enjoying the outdoor fireplace up there.
I don’t know what is up with the Chicago architectural river boat tours at this time of the year, but they are nice to take in the sights and get a bit of history about the city while at it. You may be able to get them cheaper on Groupon.
As of the last year or so, this spa place
https://beaire.com/en/aire-ancient-baths-chicago seems popular with visiting family and friends. The chain has a Copenhagen outpost too, but perhaps not a “bros trip” thing to do.