Answer:
1. "Looking down at the fathomless pit into which I was going to engulf myself."
2. "I imagined I was traveling through a hollowed-out diamond with the rays disintegrating into a thousand dazzling lights."
Explanation: He uses the words "Looking down at the fathomless pit into which I was going to engulf myself" as a metaphor to explain that he was acknowledging that in order to face his fears, he had to go through a difficult journey that would be like a "pit" (water well) to him.
Axel also uses the metaphor: "I imagined I was traveling through a hollowed-out diamond with the rays disintegrating into a thousand dazzling lights." to describe how breathtaking and beautiful the sight was when he was on the subterranean, just as he was looking at a diamond and its bright lights.