The Boca Raton Museum of Art is the cultural anchor of Mizner Park, with a collection that mixes modern and contemporary art, photography, works on paper, and pre-Columbian objects. It is not a giant encyclopedic museum, and that is part of the appeal: you can see it properly in a couple of hours.
Temporary exhibitions are the reason to check the calendar before you go. The museum pairs well with lunch or dinner in Mizner Park, making it one of Boca's easiest rainy-day or heat-of-the-afternoon stops.