The labyrinth is an elaborate maze from Greek mythology. In addition to being confusing, with many dead ends and wrong turns, it housed many dangerous obsticals. Most famously the Minotaur, a creature that was half man, half bull, lived at the center of this maze.
In literature, a heroic labyrinth is not usually a physical maze, but a symbolic one. When the hero reaches the most trying part of his journey, faces many dangers and difficult decisions as to which path to follow, it can be said that he is in the labyrinth.
D. it is a difficult part of a journey where the hero must make many choices and adventures, take high risks.