What will you find under the Paris opera?

Under the Paris Opera, specifically the Palais Garnier, you can find a vast underground network that includes a large reservoir, designed to prevent flooding. This subterranean area inspired Gaston Leroux's novel "The Phantom of the Opera," which features the iconic character of the Phantom residing in these depths. Additionally, there are various storage rooms and passages that contribute to the opera house's rich history and architectural intrigue.