Both Uses of

labyrinth
in
The Phantom of the Opera

And the Persian, asking Raoul to deaden the sound of his footsteps, led him down passages which Raoul had never seen before, even at the time when Christine used to take him for walks through that labyrinth.†
Chpt 19

Raoul followed the Persian and wondered what he would have done without his companion in that extraordinary labyrinth.†
Chpt 20 *

Definitions:

(1) (labyrinth)
a maze (a complex system of paths or tunnels in which it is easy to get lost)

or (figuratively): anything so complicated that it is extremely confusing

The word "labyrinth" comes from the name of the maze of passages where, in Greek mythology, Theseus had to escape from the Minotaur.
(2) (meaning too rare to warrant focus)
meaning too rare to warrant focus:

Less commonly, labyrinth can refer to a complex anatomical system of interconnecting cavities -- especially the inner ear