If you had some trouble solving the puzzle, here is a quick walkthrough.

The first section of the story leads you to a door with a padlock. The code to the lock is the number of words in each verse of the poem. [3455]

Cold are stones [3]

They crush my bones [4]

Living dying in the ground [5]

Never ever will be found [5]

The solution to the second part of the puzzle can be solved once you explore the cave and discover 3 clues. In the original room [meat locker], you find a map by the table with strange letters at the top. After searching the desk of the lowlit study, you find a handwritten note that gives you the name of the cave and the information that the code for the door panel has something to do with the girl and a code. Finally, by searching the small room, you find the dress with the name Evelyn stitched into the collar.

The note hidden in the desk gives you the name of the cave. Santram Cave has the same number of letters as the strange words at the top of the map. This can lead you to discover the nature of the cipher and several of the letters needed for the code. The ATBASH cipher is a simple cipher that mirrors the alphabet. If you don't know anything about ciphers, you could also have discovered this by searching and comparing simple codes [ciphers] or typing the words into a website that decodes ciphers. There was also an additional clue revealed when you took a drink of water in the tunnel where you fell in. This clue introduces the word "cipher" if you hadn't already been looking for that, and decodes the second word on the map - XZEV to CAVE. This in itself is a pretty clear indication of the ATBASH cipher, which is shown below.