Take our two (17/15) at least once a year. Things that they have enjoyed are going up in both towers, architecture tour and walk through of their museum, taking the water taxis between locations, walking the river or lakefront/beaches when it’s warm, Fields Museum, Art Institute, walking Millenium to see the fountain/Bean, the aquarium, the planetarium, walking Michigan Ave and the surrounding areas north/south of the river, seeing a show, Wrigley, and who knows what else. They always want to eat at Yolk and then Steak 48 lately.
It’s an easily walkable City, so we rarely take the trains any more. We’ll get an Uber if we are getting outside of downtown, but you can easily cover most everything with water taxi’s and walking. We have stayed at a number of places downtown, you can cover any level and budget you want. We have stayed at the Langham the last 4-5 trips because we like the location and the hotel itself.