The Boston Public Garden is right next to Boston Common. It is a lovely park with a pond in the middle. During the summer, for $3, you can take a ride around the pond on the Swan Boats, which have been operated by the same family for their entire existence. There are also statues, including one of George Washington and of the ducks from "Make Way for Ducklings." It's a nice place for a walk or to sit and relax on a hot day.
The "Make Way for Ducklings" statues.
The George Washington statue.
The Swan Boats.