here is a cool article, they actually found a cinema down there:
http://www.guardian.co.uk/internatio...299444,00.html
After entering the network through a drain next to the Trocadero, the officers came across a tarpaulin marked: Building site, No access.
Behind that, a tunnel held a desk and a closed-circuit TV camera set to automatically record images of anyone passing. The mechanism also triggered a tape of dogs barking, "clearly designed to frighten people off," the spokesman said.
Further along, the 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.