Set in some kind of (half-)sunken shipwreck. As the player explores the wreckage they discover the story of the ship and what caused the ship to run aground.
Could be set on a pirate ship, or a merchant vessel, maybe an ocean liner.
We could use concepts like limited oxygen supply and claustrophobic environments, limited vision through dark water. Water level could rise creating a dynamic level for the player to move through, raising and lowering the water level could provide some interesting mechanics for navigation, maybe resulting in situations where the player could get trapped and begin to feel panic.
Sound design would focus on eerie underwater ambiance, cracks as pressure changes, sound of rushing and moving water.
Oxygen, Light, Pressure? (depth), protection against hazardous materials?
Maybe the crew of the ship perished in tragic ways, leaving behind fragments of narrative eluding to why and how they died. Environment becomes increasingly perilous as the player progresses through different spaces.
Narrative would focus on the story of the ships crew and what caused them to run aground, player would be navigating through the environment piecing together events.