Where is he headed and what does he like? If the happy couple like mountains they should head up into the White Mountains region of New Hampshire, and be sure to head up Mount Washington. If they're into oceans, the only national park in New England is Acadia National Park in Maine. It'll be a drive -- it's 400 miles from me and I'm in southern Connecticut, but well worth the trip IMHO. Acadia is one of my favorite places in the world.
There's a lot available. There's the Nautilus submarine museum in Groton, Connecticut. Old Sturbridge Village ( a recreation of a colonial village) in Massachusetts near the Connecticut line. If they hit Boston they should take the Duck Tour. Guided (driven) city tour, but not in a bus. The vehicles are converted WW2 amphibious assault vehicles, and the tour actually goes into the Charles River basin for a short stretch. Lotsa fun.
And, of course, if they're into gambling the Foxwoods Casino in eastern Connecticut is supposed to be the biggest single casino in the world. And Mohegan Sun casino is only a few miles away.