Members of the force's sports squad, responsible - among other tasks - for policing the 170 miles of tunnels, caves, galleries and catacombs that underlie large parts of Paris, stumbled on the complex while on a training exercise beneath the Palais de Chaillot, across the Seine from the Eiffel Tower. . . [T]he tunnel opened into a vast 400 sq metre cave some 18m underground, "like an underground amphitheatre, with terraces cut into the rock and chairs".
There the police found a full-sized cinema screen, projection equipment, and tapes of a wide variety of films, including 1950s film noir classics and more recent thrillers. None of the films were banned or even offensive, the spokesman said.
A smaller cave next door had been turned into an informal restaurant and bar. "There were bottles of whisky and other spirits behind a bar, tables and chairs, a pressure-cooker for making couscous," the spokesman said.
"The whole thing ran off a professionally installed electricity system and there were at least three phone lines down there."
Three days later, when the police returned accompanied by experts from the French electricity board to see where the power was coming from, the phone and electricity lines had been cut and a note was lying in the middle of the floor: "Do not," it said, "try to find us."
Though it does make you wonder if anybody less benign is down there.