Massachusetts Audubon Society

This place is awesome!
The building is not the main attraction here. When it is open, you can go in and check out some fliers and talk to some real nice people, but the main point is the trails and activities they sponsor.
They have a great amount of trails to walk along, heading into the woods, close by farms, and right along the beach, so you get a bit of everything from these walks. They are pretty well maintained, but you should still use some bug spray to prevent ticks and mosquitos, as well as boots for there may be some mud puddles. Take your camera and binoculars for some great nature scenes and animals.
They also have many guided walks and family events, as butterfly walks or planting a a garden. Get out there and enjoy nature!