Hey, it's good to see that you're still working on a trip to MA!
If you're still heading to the Cape, I would suggest looking in Provincetown. I wouldn't be too concerned about heat/humidity here. There are maybe 2-4 days per summer where it's miserably hot/humid and that's about it. The Cape, as others have mentioned, is a bit better in this regard. Evenings on the Cape are gorgeous. It usually stays between 70 and 80 and there's always a breeze.
In Provincetown, you should do obviously walk around the center of town (along Commercial Street) and the wharves. I would also check out the
P-Town Tower/ Pilgrim Monument. This is a cool climb (a 200+ foot tall granite tower) which gives you stunning views of P-Town, Cape Cod, Cape Cod Bay, The Atlantic and even Boston on a clear day. There's also a museum at the base which is interesting as well.
A trip to Provincetown isn't complete without a
Whale Watch. This is a must and there's nowhere better in New England to do a whale watch from than P-Town. Before you get on your whale boat, grab a pastry from the little Portuguese bakery adjacent the wharf.
Since Provincetown is the tip of the Cape, an excellent place to relax on the beach is Race Point Beach (the actual "tip" of the Cape). Not only is this a cool beach to relax and enjoy the water at, but there are a number of old lighthouses that dot this area that are fun to explore. It's a great area. In fact, near P-Town you have the whole
Cape Cod National Seashore which is fun to explore.
If you want to take a day trip to Boston from P-Town, it's over a 2 hour drive. There is, however, a better way to do it. Bay State Cruises offers a 90 minute
fast ferry from P-Town to Downtown Boston which is wonderful. Boston is so walkable that you don't need a car. The ferry allows you to avoid parking (which is a pain and upwards of $30+ a day) in Boston and take a much more scenic route. You can spend the day exploring Boston and then return to P-Town at night.
If you have a car (and for the Cape, you'll need it), you may want to leave the Cape for a bit. Plymouth is a cool town with a lot of history. You can explore
Plimoth Plantation or the
Mayflower replica and explore the town center and waterfront.
New Bedford is also a cool day trip. Not only are 16 blocks of the downtown area part of a beautiful
National Park, but there are a ton of art galleries, shops, and restaurants. There's a ton of history in New Bedford. Herman Melville wrote his book, Moby Dick while he lived and worked for a New Bedford Whaling company and many of the landmarks described in his book are open to the public in town. The
Whaling Museum is a must see while in town. There's a brand new
Ocean Explorium which is still only partially complete but it's worth a visit anyway. You may want to head across the street from the Whaling District and check out the Waterfront. It's home to the nation's highest grossing fishing fleet and it's fun to watch the fishermen work. Also on the waterfront is the
Waterfront Grille, some of the best seafood in New England outside of Boston. A show at the
Zeiterion Theatre or a visit to the small, but fun
zoo may be interesting too.
New Bedford is ripe with cultural diversity. It's mostly known for it's thriving Portuguese heritage. A trip to the area without exploring this would be a big miss. New Bedford has TONS of Portuguese restaurants and I would suggest visiting at least one.
Antonio's,
Adega,
Cafe Funchal, or the
MandC Cafe are some favorites of mine. The
Feast of the Madeira in New Bedford is an awesome time to go. It's Old World Portugal at its finest. There are over 300,000 visitors to this feast each year (the largest in the world of its kind) and there are concerts, wine vendors, artists, etc all in the streets. if your trip coincides with this, check it out.
Anyway, there's plenty to keep you occupied. Enjoy your trip!