For Martha's Vineyard, it's a lot of fun to rent scooters.

If you're interested in historical sites, I'd recommend Plimoth Plantation, Old Sturbridge Village, and the Freedom Trail in Boston. There are a ton more, of course, but those are the ones that stick out in my memory. If you're really into old ships, Mystic Seaport is good, but I think Sturbridge is better for that kind of experience. If you're into naval history, Battleship Cove at Fall River is really well done.

If you just want to hang out with nature, there are a ton of places to do that. Vermont is practically uninhabited, so you can go just about anywhere there. Once you get past the greater Boston area, New Hampshire is pretty sparse as well, as is Maine.