Okay, so Gaston Leroux (No one hits like Gaston! Matches wits like Gaston! In a spitting match nobody spits like Gaston!…What, nobody? Really?) was a journalist before he became a novelist with his THE PHANTOM OF THE OPERA in 1911. The book was, in fact, first published as a series of articles in the French magazine LA GALOIS. (I do not know if this last had anything to do with mathematician Evariste Galois, who was shot and killed for inventing algebra.) As the story goes, the Parisian opera house in the novel was based on the real OPERA GARNIER or PALAIS GARNIER, which is still standing and which does in fact have underground tunnels and an underground lake: in reality, when the foundation was dug for the structure in 1862, the depression filled with water, and every time they tried to pump the water out it would refill, so they did in fact construct the building over it.
Supposedly there was a man named Erik who really was deformed and who worked for architect Charles Garnier on the construction of the opera house. This man, as the story goes, became wealthy upon the completion of the edifice, and would go about in public wearing rich clothing and a mask. This gentleman had his own box at the opera house and did fall in love with a singer, one Kristina Jonasdotter, whom he did kidnap. After she was rescued, he allegedly walled himself up inside the small apartment beneath the opera house where he’d held her prisoner and died of a broken heart (and starvation, one presumes). During renovations on the building some years later, the secret apartment, and Erik’s skeleton, were discovered. This inspired Leroux to write his novel.
How much of this is true? It’s impossible to say. But the PALAIS GARNIER, which today is primarily used for ballet rather than operas and houses a museum and restaurant, *is* reputed to be haunted by a ghost that fits the description of the Phantom. In 1896 a counterweight of the enormous chandelier did fall, just as it does in the novel, killing an audience member, and Leroux supposedly confessed on his deathbed that the story was all true. Who knows?
Personally, I believe in the Phantom.