An example of an undersea facility.
Poseidon Base was an undersea military facility located on the seafloor about 1,000 miles east of Hawaii, established in the mid-1990s.
It was run by an AI named AIDAN and crewed by Navy personnel; after skydark, AIDAN received new orders and attempted to asset control over the station by breeding the women to create a sustainable population. The crew revolted and were killed or turned into cyborgs under AIDAN's control; the companions destroyed the place by breaching the hull in multiple places and flooding it. (Dark Fathoms)