Saltwater marshes, maritime forests and 18mi of lonely beaches compose the complex ecosystem that is Cumberland Island. The largest and least developed of Georgia's Golden Isles, the island lies across Cumberland Sound from the town of St. Marys, Georgia. Stately 1898 Plum Orchard (visit by guided tour only) and the 1884 Dungeness—of which only eerie ruins remain—were both once occupied by members of Pittsburgh's monied Carnegie family.