You can't throw a stone in Massachusetts without hitting a historical site but one of the best I've been to in a while is the Minuteman National historical Park in Lexington. We were lucky to have a nice day during a cold November so we took advantage of it and headed over to the park. it's a great place to walk around with a ton of history but the highlight is the statue that marks the site of the shot heard round the world.
Lexington itself is really nice, so make sure you stop in town. If you need me excuse there's a great coffee shop!