Down a hole in the corner of the building at spawn there is a painting. If you throw an item on a pressure plate behind the top left block of the painting the door will open. There's an armor stand, lava, and a sign that days "safehouses"
ReplayEMC --------------- Looks like "safehouses" was the 4th and final key, and the decoded message reads, "The time has come. If you have found all of my messages there is nothing I can do to stop you. Come to my bunker and I hope you bring good will. myBunker" Then I used the loc, "myBunker", to arrive at this room:
That seems like an interesting puzzle! I don't like how the res needed to be edited in-between, though.
The editing was meant to create some of the story I wanted around this one. In the future I will definitely try to avoid that though.