They raised the streets to get them out the swamp that Chicago was built on. If you go to downtown Chicago the city is built up about 20 ft. It’s really visible at the river bridges, or union station, the bridges over the river are flat, and the trains go flat into a basement. Prop who live in those houses can have storage under the sidewalk, and they were often the site of the outhouse in the late 1800s. It’s a fascinating read the raising of chicago
I’ve been to Chicago many times. I always thought that the sections under Michigan Ave, like where the Billy Goat Tavern is IIRC, were just built that way.