Is there anywhere close to Boston not to be missed?
Lots of great stuff near Boston.
We'd need to know what kinds of things you like to do before we can make suggestions. There are museums, hikes, sports, shopping, active experiences, etc, etc, etc. What's "not to be missed" for you probably isn't the same as for me
How do you define "close to Boston?" Just how far are you willing to go and what do are you interested in doing? One persons "not to be missed" may not work for someone else.
Depends on your definition of close and the time of year you are coming, and of course your interests. For some visitors New York City would qualify as close (it's 4 hours away). Likewise the Cape Cod National Seashore might be a not-miss attraction, but not in February. I love the Boston Harbor Islands and the view back to Boston, and a lobster roll at James Hook, but everyone's idea of not-to-be-missed will differ.