As the title suggests, its an idea for a mod that adds what is basically the human equivalent of alien ruins.

The "Sea hulk" would be in amalgamated mishmash of several submarines stuck together, rich with resources but always full of danger.

For example if they spawn similarly to how hostile ships spawn the primary danger would be trying to keep the thing neutrally buoyant as you loot it, lest it go plummeting into the abyss, plus the dangers of local wildlife, husks or cultists aboard.

perhaps a button that opens the door is also wired to a depth charge launcher elsewhere inside the the hulk, because what was once the external Hull of one submarine has now become the ceiling of another.