Then you don't know the best part of the country!
My wife and I will fly into Providence in October, we plan to take the train into Boston and see the sights. Any recommendations will be appreicated, we will be in Boston 7 days. Then we'll take the train to Philadelphia (where I've been but L. has not) and then down to Richmond, VA. We'll fly home out of N. Carolina.
You gotta go to the Charlestown Navy Yard and tour Old Ironsides. If you get there at dawn or dusk you can see them fire the cannon before raising or lowering the flag. From there, hop the ferry over to Faneuil Hall. You could go to the aquarium right where you get off the ferry, or cross the street to Faneuil Hall itself and hit all the little shops and stuff. If you are hungry while there go to the Union Oyster House - oldest restaurant in the country and a former fave of JFK (you can see 'his' table there) - expect a reasonable wait depending on the time of day. Right out in front you can see the statue of Red Auerbach, or the Holocaust Memorial if that's your thing. Near the Union Oyster House is a bar called the Green Dragon, another historic site. Paul Revere and John Hancock used to put back brews there and plot rebellion. They serve a nice shepard's pie and often have live music. From there it's a short walk to the North End where you can get some very good Italian food (do NOT try to drive to the North End as you WILL get trapped in an infinite loop of narrow one-way streets and construction detours, and anyway it is all but impossible to find parking there (only chumps pay to park in one of those huge parking garages).
Unfortunately, you will be too late to ride the Swan Boats in the Public Garden, but you should still go to Boston Common. You can check out the State House and then walk to Chinatown for some grub (Peach Farm restaurant is a personal fave). Do NOT go to Chinatown after dark (for the most part it's ok but I wouldn't want to push your luck). From Chinatown you can walk to the waterfront and try good, pretty cheap seafood at The Barking Crab.
If you've got time, hop on the Blue Line all the way to the end (Wonderland) and walk up Revere Beach (not so beautiful, but the first public beach in America) to Kelly's Roast Beef. You have not been to the Boston area without eating at Kelly's. There are a few bars along the beach, but don't go to them unless you can handle yourself and are not timid.
Take a trip into Cambridge and gawk at the feaks in 'the pit' in Harvard Sq. Head to Kenmore Sq. to see Fenway Park (100 years old this year).
The Duck Boats are a popular touristy thing to do if you want. You could go to the Museum of Science first since they depart from right out in front.
The Museum of Fine Arts is also nice, but again don't hang around that neighborhood late at night.
If you can, I'd also recommend heading a bit north to Salem for a day. Lots of interesting stuff up thataway.
Anyway, there's lots more. Let me know if you need further recommendations.