Question: Where did the phantom of the opera live?
Disambiguated questions and answers: question: Where did the phantom of the opera live in the original novel?
Where did the phantom of the opera live in the 2004 film?
answer: the Palais Garnier opera house
his lair
his underground lair
the theatre
Natural Questions answer: the Palais Garnier opera house (from the Wikipedia article "The Phantom of the Opera")