Bring sugar and water to a boil in a very small saucepan, stirring until sugar is dissolved, then boil 1 minute. Stir together raisins, rum and sugar syrup in a small bowl, and let raisins plump, covered at room temperature overnight.
Cut peel from grapefruit, including all white pith, with a sharp knife and cut sections free from membranes. Put sections in a serving bowl and pour rum-raisin syrup over them. Sprinkle with almonds.
Recipe courtesy of Gourmet Magazine