It was the entrance to the Cour de l'Administration.
Raoul rushed into the doorkeeper's lodge.
"I beg your pardon, madame, could you tell me where to find a gate or door, made of bars, iron bars, opening into the Rue Scribe ...

and leading to the lake?
...

You know the lake I mean?
...

Yes, the underground lake ...

under the Opera." "Yes, sir, I know there is a lake under the Opera, but I don't know which door leads to it.