It's only eight miles to Darby Island, leaving you plenty of time to explore a 7,000-square-foot castle built in 1938 by a Nazi sympathizer. A trench dredged out by the Englishman to harbor U-boats is good for drift snorkeling and spearfishing bar jack. Cook them up that night at camp on the western side of Darby. Add coconut husks to the campfire to keep the biting no-see-ums away.