First Friday, monthly, evening. Openings cluster on South Division and in the neighbourhood corridors. It is the only night of an ordinary month when a gallery crawl here works, because on any other evening you are looking at locked doors. Costs nothing.
Festival of the Arts, early June, downtown, free. The city's long-running free arts festival, which has run since the early 1970s and took Calder's own "Festival Sun" design as its emblem — a direct descendant of the enthusiasm around the 1969 dedication. Stages, food stalls run by community groups, and a lot of children covered in paint. It is a festival first and an exhibition second, and it is the friendliest weekend of the year downtown.
ArtPrize, mid-September into early October. More than a thousand entries across the whole downtown, free to walk, and the single busiest art fortnight in the Midwest. It has its own page on this site because the practicalities — where to stay, where to park, how to walk it without seeing four hundred bad paintings — need the room.
Outside those, the answer is the public work, which never closes, and the two collections, which run year-round. February is the quietest month in every gallery in the city and the best month to have the Maya Lin rink at night more or less to yourself.