Police in Paris have discovered a cinema complete with restaurant and bar in a cavern underneath the city.

Officers admit they are at a loss to know who built or used it, reports The Guardian.

"We have no idea whatsoever," a police spokesman said.

"There were swastikas painted on the ceiling, but also celtic crosses and several stars of David, so we don't think it's extremists. There are any number of possibilities."

A mechanism had been installed that triggered a tape of dogs barking, "clearly designed to frighten people off," a spokesman said.

Police found a cinema screen and films, including recent thrillers.