You are going to:
And the Safe combo is:
I had no idea where to start with this, so did some cryptanalysis. The Index of Coincidence was $0.04082$ suggesting a polyalphabetic cipher (therefore likely vigenere), and running probable key lengths suggested that the most likely key length would be 8. Now things started to fall into place!
The first important ...
The word is
The emphasis in the puzzle on visualizing the audio motivated a spectogram of the audio revealing
which combined with the Sherlock reference immediately brings to the mind
In this short story, the antagonist uses
to encrypt messages. Though the original publication doesn't reveal all the letters - and one may have some fun trying to figure ...
I can't solve the entire message, but here's a start. I'm happy for someone else to take this idea forward in their own answer.
The encoding works - at least in part - like this:
Unfortunately for me, I've not been able to make any more progress after that, and it doesn't help being on a mobile either!
I have a suspicion that this bit of the puzzle:
To continue on from @Phylyp's work - they were first to realise the encoding mechanism for the message:
Using a very manual approach to the decoding, assisted by some Excel formulae which allowed me to keep tabs on the current possibilities for each letter, I have now fully decoded the initial message (punctuation mine):
What next? Note ...
Got it! You made an excellent breakthrough in your answer. I shall follow on from your progress to show you how this puzzle is solved and provide you with all the components for the final answer, although in the spirit of geocaching I shall not post the full coordinates explicitly here on the Internet, just give you the pieces to put together...
First, you ...
Here's what I have so far:
The Penguin Breathed refers to a penguin named Opus from a comic by Breathed.
Opus as in musical compositions that have that name. The first word of each penguin sentence is the name of an Opus. Here's what I got so far:
Impromptu 90 or 66
Be Eagle: 157 maybe
"in the woods" maybe 109