Question:  The House of Atreus Act I, released in 1999 is the first part of a metal opera inspired by the  only extant example of an ancient Greek theatre trilogy which won first prize at what festival?
Sentence (from "The House of Atreus Act I"): The House of Atreus Act I, released in 1999, is the ninth studio album by the American heavy metal band Virgin Steele.
Relevant evidence: Yes