If you appreciate history at all, walk the Freedom Trail. It's a route through downtown Boston denoted by painted footsteps on the street, goes by most of the early Boston, revolutionary, and civil war sites. Very interesting. I especially enjoyed the old granary cemetery. It's downtown on the route. Gives you a sense of how people lived and died over four centuries ago.
Rent a car and drive up to Salem, visit the witch museum. I found the "Cheers" bar definitely underwhelming and would not bother.
I've always been there on business and stayed in standard hotels like the Westin, but I had someone recommend this as a great little place: In Beacon Hill just off Boston Common. Great location.
http://beaconhillhotel.com/