It can be unlocked as a workshop settlement by completing Walk in the Park with Old Longfellow. The entire island counts as the settlement, and there are loads of dead trees to provide wood. The island also has lots of arable land for crops, plenty of room for new buildings, and open water for large scale water production.
The island is decently sized and has a cozy cabin in the center. Just beyond the front porch is a cooking station, and behind the cabin in a shed containing the settlement workshop, a power armor station, and a weapons workbench.