Hundreds of sea turtles nest on these beaches in spring, wild boar and alligators make this their home, and it's common to see armadillos trundling through the underbrush. The human footprint here is equally varied and fascinating: Native Americans lived here as many as 4,000 years ago, the Spanish built several missions here in the 1500s, and in the 1880s, Thomas M. Carnegie and his wife, Lucy, came here and built the 59-room Scottish castle they called Dungeness. Its ruins and outbuildings today still stand as wild ponies graze on the once-immaculate lawns. On our first visit here, one of the rangers encouraged us to hike past Raccoon Flats, where there were massive mounds of dirt; it was old dredge spoil from the channel. Here, he said, we'd literally trip over fossilized shark teeth. Since then, fossil hunting has become one of our favorite pastimes here, and on a good day, we might return to Osprey with a whole spice jar full of teeth of all sizes and shapes. It costs $4 per person to stay here for seven days (it's free for children under 16), paid in an honor-box system located at the head of the dock. Like Cape Lookout, this island is accessible only by ferry, and when from Osprey's cockpit I watch the last boat of the day leave, I always feel supremely lucky to be able to stay. Also like Cape Lookout, it has a handy town nearby—Fernandina Beach, Florida, which is only five miles to the south—where you can take care of the cruising necessities before you come here for pure peace and quiet.