It appears this place was used as a last resort for glowies and 'luminaties. They have some sort of dimensional fuckery going on around this Mariana Trench location. It seems to be hiding parts of the Earth, similar to how the real "Africa" was hidden behind the gate at Antarctica.

I copied and refined the symbolism and methodology used to access these dimensions, feel free to crash the party. Ask for "Mariana". Just be warned, if you are insecure about this stuff, you have to use the form of a dickgirl/trap to enter here. This may be why the elites are into this stuff.

It's not that you have to actually change, but your astral image needs to be a male wearing a dress (or general 1700s aristocrat clothing) and armed with a very thin fencing sword/dagger of the era.