What are some fun things to do in Boston?

I'm heading to Boston for an overnighter next month. I'm going to see "The Blue Man Group" at the "Charles Playhouse". I'm going down with a ladyfriend, so... Any advice will be much appreciated.

I used to live up there. There's a lot to do. A few highlights would be Faneuil Hall, the gardens, some of the Freedom Trail, Harvard Square, Back Bay, the North End for good Italian food. Great clubs and bars in the Faneuil Hall area and Landsdown Street.