It was this condo, in East Lakeview.
https://www.google.com/maps/place/23...1!4d-87.638367
Yeah, it was five floors, definitely walkup, and (I think) two units per floor. This exact small-building typology doesn't seem to exist in NYC, for whatever reason. At the least there would be an elevator, and boutique condos tend to be one unit per floor, as the lots are typically smaller.
Are the higher floors in walkup Chicago condos cheaper? I guess that would make sense, though the top floor probably (?) has rooftop access and at least no noise from above units. I don't think I'd want a 5th floor walkup, though (though this might technically be 4 floors if they count the ground unit as a basement level or something, as it's clearly somewhat below-grade).