If you do go to Salem make sure to check out the Witch Dungeon Museum. there is also a Witch Museum, but I think the Witch Dungeon Museaum is far more interesting and better done.
I love Salem...very intersting. Agree Duck Tour of Boston would be fun. Don't forget taking a ride to Concord and/or Lexington. I first visted Boston when I was around 14 and found it facinating to see stuff we studied in history. Not sure how much the revolution or the american colonial period is studied where you are. Walden Pond is in Concord, as well as Louisa May Alcott's home.
walk the freedom trail in Boston...check out the old north church, and walk up behind it to the old cemetary...there is the thinnest house right across from it! Anther cemetary is called the granary, and is right near the common. Really interesting...Mother Goose is burried there, victims of the Boston Massacre, Sam Adams. John Hancock, among others. To connect your salem trip, there is also the judge (?) that was involved in the witch cases buried there.
Enjoy your trip to Boston!