This is a cool monument to the old Olympic Park. I think Montreal was one of the only cities (if not THE only) to design their Olympic facilities with the future in mind. This park still has museums, attractions, and a public sports facility open to all residents. They reused all of the buildings for something and they are open to the public now. There's also a ton of green space and areas for picnics, walks, sitting, etc. Really, Montreal thought the Olympic thing through and got the most out of what they built for it.
It's easy to bike here or take the train and there's tons of bike parking and there's a BIXI station right on the grounds so you can rent and park. There's a fair amount of things to do here and other attractions nearby so you can fill an afternoon visiting. I highly recommend, especially if you want to learn about the Olympics or the Expos (les Expos nous manque!).