If you’re headed to the Cape, don’t forget to stop in the Fuller Craft Museum in Brockton (quick stop off Route 24). They have some great exhibitions right now, including a large collection of glass art from MIT. According to Wikipedia, the museum’s architecture and gardens inspired the Louisiana modern art museum in Denmark.
Reasonably good for kids (we went with a 4-year-old and she was losing interest after about 45 minutes).