Possible Clues:

• Wagner work
• Musical work parodied in Looney Tunes' "What's Opera, Doc?"
• Wagner opus
• O, go for a ride to see cultural event!
• Wagner work ... or a possible title for this puzzle
• Quartet of Wagnerian operas, and a hint to the progression in this puzzle's circled letters
• Call round for four evenings of music
• Musical work in four parts, with its first part opening the Met's 2010-11 season
• Wagner creation
• It was parodied in Looney Tunes' 'What's Opera, Doc?'