People tend to check in during these times:
Big time dog park. Great place for some off leash fun.
Diamond in the rough
Lots of hidden playgrounds and pretty gardens. Awesome view of the Bunker Hill Memorial Bridge.
Since this is basically a dog park, bring the pup here after dark and enjoy the stadium style lights!
A pleasant park with a decent playground and good open lawn space, just over the Charles River Dam from Boston proper.
The short siren means the railroad bridge is about to go up.
You can cross the river here on foot by walking across the locks.