Someone recommended I post this here. My friends and I found our way into the Moon Bunker.

My friends and I found a way to fall through the map behind the old spawn point in Archer's Line and got into the Bunker.

I took some screenshots of the inside.

I can go back and take more screenshots, or attempt to explain how I got into it.

Edit: Here's a video of how I got in.

Edit2: Here's a post of how others got in. Their way is much much easier, I recommend their way if anyone wants to try it. Props to u/Pirogoeth_ and u/Bachmanetti