Peter F. answered 09/24/20
Well-read Upper School English Teacher; 18 Years' Teaching Experience
Hi Jane,
I think that in this case, mysterious cave refers to the idea/metaphor that darkness can last and go on forever, make you feel lost and lonely inside, and cause you to hear echoes of your own voice and thoughts inside your mind as you continue to travel down the scary, sometimes risky and dangerous path of everyday life.
I hope this helps!