Darkness file

Firstly, the song is not quiet, it resonates, but this is perfect for the dark mysterious atmosphere you are talking about.
It gave me the sense that I was inside of a very dark cave with very low visibility.
The only thing that I didn't like was the added sound that sounded like a glockenspeil (however you spell it), it took away the mystery, perhaps a more subtle and more eerie sound would be best to take it's place.

Otherwise, I enjoyed this track, it kept me interested and had the effect that you said it had.