People tend to check in during these times:
Big time dog park. Great place for some off leash fun.
Diamond in the rough
A pleasant park with a decent playground and good open lawn space, just over the Charles River Dam from Boston proper.
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!
Nice place to walk your dogs and play
Large park, great views, water fountain in play area. Plenty of benches and garbage cans. Some riff raff but mostly runners, people with babies or dogs. Lots of photographers
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.