Mystery Bay State Park is a small Washington marine park on the western side of Marrowstone Island along Mystery Bay, a sheltered inlet off Scow Bay and Kilisut Harbor. Covering 18 acres about half a mile north of the Nordland General Store on Flagler Road, it is defined by its close relationship to the water. Older wooden sailboats at permanent moorage give the shoreline a strong maritime character. The park offers picnicking and beachcombing on land, while the bay supports boating, fishing, shellfish harvesting, and scuba diving. Its importance lies in providing quiet access to one of Marrowstone Island’s protected inlets.