Visit a New Park
This isn't a specific place for an activity but an idea that my kids love to do. We sometimes go to a different park in a different neighborhood and have a great time simply because it's new to us. Some great parks to try are Westmount Park- lot's of green space and plenty of park equipment. Lasalle Park in Lachine - two pools, lots of green space, tennis courts, skateboard area. Girouard Park in N.D.G.- great new facilities including a fun new water play area. Parc Lafontaine is a big park with lots of green space, manmade lake with ducks and great park equipment. Go out and explore because sometimes it's just fun because it's new to you.
Here's a list of some parks from wikipedia: