Dundonald Park takes up a full city block in Ottawa's Centretown. Until recently, it was fairly neglected, but efforts to make it a more welcoming place have paid off. Now this is a vibrant urban greenspace.
In the summer you can view pay-what-you-can movies in the park during the Centretown Movies film festival. The park is also extraordinarily photogenic when the autumn colors come out. It's definitely worth a visit when you're looking for a place to spend the day outside.