I see nobody dares to move forward..Let me help with a handy time skip
A short while later the sub is back to the spot you were earlier...just a few hundred meters lower.
As you arrive this time with a sub under your own control you can see the outside of the base.
From the central part eight pipes spread outwards.
Only that these pipes seem to be made out of hundreds of overlapping parts. Hinting that they might not be so much actual pipes bt some sort of legs.
On land you would say they are too thin to lift the base, but as it is air filled it might be enough to move it under water.
It might also just be a flawed design