G-Deck
G-Deck is the lowermost accessible deck on the Titanic. It is only accessible to the crew, and contains the Turbine Room and Engine Rooms, the Control Room, the Boiler Rooms and the Cargo Hold. Through G-Deck, one can also access the top of the False Smokestack.
There are two ways into G-Deck: via a stairwell by the Second-Class Cabins on F-Deck, or via the Forecastle Deck, that leads into the Cargo Hold. There is also a door that leads from the Engine Room to Scotland Road, but it will only open from the inside.
While all of G-Deck is accessible in the first half of the game, only the Turbine Room is accessible during the sinking - attempting to enter the Control Room will result in Carlson being stopped by a crew member and instructed to get back up top, as the boiler and engine rooms are flooded.
Vlad Demonic, a stowaway, is only ever encountered on this deck, however he always escapes the Titanic regardless of the ending achieved.