The great dome of the Opera Garnier, home to several dance halls, each with its own piano. The most prestigious occupies the entire area under the green dome. The floor of the ballroom is inclined to replicate that of the theater. A sloping floor allows the public to see the choreography. For some shows, you need a flat surface. It then adds a platform.

Source: words collected from a former manager of the opera.

The walls of this quarry are particularly whites because they have been limed. We also see the flashes of lime to the ceiling which clearly shows a projection method of liming.

Quarries of Paris - The network located in the Val de Grace hospital.

Beside the stairs Mansart, whose name was chosen in reference to the architect François Mansart, author of many works of consolidation in the hospital of Val de Grace.

A plate shows the depth of the underground quarry with great precision: Height 58 feet 6 inches or 18 meters 9969.