Wagner’s sixth opera, “Lohengrin,” tells the medieval legend of the Knight of the Swan: the knight Lohengrin is sent to protect Duchess Elsa of Brabant, who has been unjustly accused of murder. Johannes Erath directs the production, and Joana Mallwitz conducts the orchestra. Piotr Beczała plays the title role. Rachel Willis-Sørensen plays Elsa of Brabant.