Your questions are so general that it's hard to make recommendations without knowing what you like to do and what sort of food you want. Museums, history, shopping?

On your other thread you ask about the weather. The end of March can be pretty iffy--it's hard to predict but be prepared for rain and cold. Then?hope for better weather.

Will you have a car?

Just Boston - or the whole state? How long will you be there?

Late March is still really winter - or the beginning of mud season. Outdoors won't look like anything yet. And many sights outdoors will be either closed or operating on short hours/and perhaps only weekends.

What are your interests.

What type of food do you like/dislike and what is your budget?

take a duck tour. Walk the freedom trail. Visit the USS COnstitution. Take a food tour of the north end. Take a Fenway park tour. Visit the museum of fine arts, the Isabella Stewart Gardner. Take a docent tour at the Boston Public Library. Go to the aquarium Visit the Science Museum. Take an irreverant tour of Harvard. Walk around MIT looking at the architecture. Visit Faneuil Hall. Shop on Newbury Street. Go to a Boston Symphony concert. See a play or other show such as Boston Ballet, Boston Lyric Opera, American Repertory Theater, Huntington Theater, Broadway in Boston, Boston Chamber Music society, Handel & Hayden, pop/rock/other concerts at the Orpheum, TDGarden, House of Blues. Hear some jazz at Scullers or the Regattabar or maybe Berklee. Tour the Old North Church and the Paul Revere house. Visit one of the breweries and taste local beers.

Does any of that help?