Christine Goerke is focused on endurance. The dramatic soprano is tackling one of the most challenging roles in opera: singing Brünnhilde, the Valkyrie maiden warrior, in Richard Wagner's epic, Der Ring des Nibelungen, at New York's Metropolitan Opera. Otherwise known as the Ring cycle, the 16-hour saga spans four operas and tells the story of gods, monsters, humans and an insatiable urge to own an all-powerful golden ring.