This was made as an extension for my complete Collection walkthrough. This contains a guide to obtaining the last non-story achievement. This was put into a separate guide because of how complex it is.

A video walkthrough is planned in the future. Stay tuned!

(Also, I was cage fighting the character count.)

Here's how this puzzle works. There are three significant locations on your map: the cabin, the hotel and the chapel. Each of these locations has another set of coordinates that can be seen through the periscope. The three new locations will each have a part of one final set of coordinates outside the right window.
Cabin: Head to the cabin (X:6 Y:6 D:0) and look through the periscope to find the second set of coordinates. Travel to this set (X:3 Y:9 D:50) and look through the right window. The coordinate (X:11) can be seen on the right of the top eyelid.
Hotel: BE CAREFUL NAVIGATING HERE, AS YOU MAY ACCIDENTALLY HIT THE DESIGNATED COORDINATES, LOCKING THE SUBMARINE IN PLACE. IT IS RECOMMENDED THAT YOU SET YOUR DEPTH BEFORE MOVING. Head to the hotel (X:6 Y:3 D:0) and look through the periscope to find the second set of coordinates. DO NOT TRAVEL TO DEPTH 50, AS THIS NEXT SET IS RIGHT ABOVE THE DESIGNATED COORDINATES. Travel to this set (X:3 Y:4 D:20) and look through the right window. The coordinate (Y:5) can be seen next to the tail.
Chapel: Head to the chapel (X:2 Y:7 D:0) and look through the periscope to find the second set of coordinates. Travel to this set (X:8 Y:1 D:0) and look through the right window. The coordinate (D:30) can be seen on the left leg of the mermaid.
Box: Head to the final set of coordinates (X:11 Y:5 D:30) and look out the right window to see a box with a code on it. Enter the code (RAT) to get the box. Using the code from Roots (and technically Birthday), enter Dale's birthday (18 12 30) and open the package inside. If you came from my Collection guide, click here to return to that.

I believe I have everything covered so far. However, in case there is anything I missed, or you have suggestions to improve on this guide, please let me know in the comments. Any criticism/help is welcome and strongly encouraged, even if it's something small like a spelling/grammar error. :)

Thank you for taking the time to read my guide. Hopefully your brain is still... somewhat intact.