" In 1910 Leroux had his greatest literary success with Le Fantôme de l’Opéra (The Phantom of the Opera). This is both a detective story and a dark romantic melodrama and was inspired by Leroux’s passion for and obsession with the Paris Opera House. And there is no mystery as to why he found the building so fascinating because it is one of the architectural wonders of the nineteenth century. The opulent design and the fantastically luxurious furnishings added to its glory, making it the most famous and prestigious opera house in all Europe. The structure comprises seventeen floors, including five deep and vast cellars and sub cellars beneath the building. The size of the Paris Opera House is difficult to conceive. According to an article in Scribner’s Magazine in 1879, just after it first opened to the public, the Opera House contained 2,531 doors with 7,593 keys. There were nine vast reservoirs, with two tanks holding a total of 22,222 gallons of water. At the time there were fourteen furnaces used to provide the heating, and dressing-rooms for five hundred performers. There was a stable for a dozen or so horses which were used in the more ambitious productions. In essence then the Paris Opera House was like a very small magnificent city.
During a visit there, Leroux heard the legend of a bizarre figure, thought by many to be a ghost, who had lived secretly in the cavernous labyrinth of the Opera cellars and who, apparently, engineered some terrible accidents within the theatre as though he bore it a tremendous grudge. These stories whetted Leroux’s journalistic appetite. Convinced that there was some truth behind these weird tales, he investigated further and acquired a series of accounts relating to the mysterious ‘ghost’. It was then that he decided to turn these titillating titbits of theatre gossip into a novel.
The building is ideal for a dark, fantastic Grand Guignol scenario. It is believed that during the construction of the Opera House it became necessary to pump underground water away from the foundation pit of the building, thus creating a huge subterranean lake which inspired Leroux to use it as one of his settings, the lair, in fact, of the Phantom. With its extraordinary maze-like structure, the various stage devices primed for magical stage effects and that remarkable subterranean lake, the Opera House is not only the ideal backdrop for this romantic fantasy but it also emerges as one of the main characters of this compelling tale. In using the real Opera House as its setting, Leroux was able to enhance the overall sense of realism in his novel. "
― David Stuart Davies , The Phantom of the Opera