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 "Alcmaeon in Corinth"): Alcmaeon in Corinth (Ancient Greek: Ἀλκμαίων ὁ διὰ Κορίνθου , "Alkmaiōn ho dia Korinthou"; also known as "Alcmaeon at Corinth", "Alcmaeon") is a play by Greek dramatist Euripides.
Relevant evidence: No