Dungeness Castle ruins is the most striking structure on Cumberland Island. Built by James Oglethorpe in 1736 as a hunting lodge, the site was rebuilt as a replica of a Scottish castle by Thomas Carnegie in the 1880's. When Thomas died in 1886, his wife, Lucy, continued using Dungeness. Eventually the castle fell into disrepair. A fire ravaged it in 1959, leaving only a skeleton. The Carnegies later deeded most of their land to the National Park Service so today 90% of the island is part of the national park. The Carnegies specified that the land was never to be developed and remain preserved as a national treasure. The former castle's lawn is one of the most likely places to find some of the feral horses grazing.
If you go:
Ruins are included in national park entrance fee.
Links:

south end of island
Cumberland Island, Georgia 31558 USA
Phone Numbers:
Park office
+1 (912) 882-4336
+1 (912) 882-4336