Best places to visit just outside Boston. Nantucket/Cape Cod?

Am visiting Boston in September, and have been before so have done most of the sights in the city itself. Am wondering where the best places outside of Boston (but doable in a day as have hotel in the city booked already) are to visit? Can you, for example, do a tour of Martha's Vineyard, Cape Cod and Nantucket in a day, and is it worth it anyway? Any other ideas most welcome! Thanks.