Welcome to city of St. Marys, Georgia! Access to Cumberland Island National Seashore. Cumberland Island National Seashore is a beautiful, largely undeveloped 36,000-acre barrier island. Access is by ferry or private boat. Fun Things To Do: Visit, the Plum Orchard Mansion and the ruins of Dungeness Mansion. Tour the Ice House History Museum and nature trails in the Dungeness area. There is walk-in camping at Sea Camp and four back-country sites. From ancient mountains to rolling rivers, charming towns to a bustling metropolis, Georgia offers whatever it is you’re looking for.