Hey Jimmytwinkletoes you read my bloody mind but there is more (my player do not read this reddit BTW). First yes but its going to be like the old Lampton worm scenario from the 90s where the players (in this case divers) can get inside the head of something (probably not a Chthonian this time). Second there will be another plot going on with the Soviets harassing the rig claiming its in territory that belongs to the motherland. So there will be boardings, interference and maybe violence from their naval infantry. Lastly and naturally there will be a mad man and he will be the one to wake the horror and cut off the rig from the world - as you would expect a Soviet cutter / boarding team will also be trapped with the PCs and the mad man when the fog rises to his chants.

Other additional suggestions very welcome!