Question: What annual Austrian society event which takes place in the building of Vienna State Opera in Vienna was featured in the made-for-TV movie Opernball?
Sentence (from "Opernball (film)"): Opernball "(Opera Ball)" is a 1998 made-for-TV movie by Urs Egger based on a 1995 novel by Austrian writer Josef Haslinger in which thousands of people are killed in a Neo-Nazi terrorist attack taking place during the Vienna Opera Ball.
Relevant evidence: Yes