A secret door? I have seen some ships keep firedoors to stairwells closed on some decks that if you open them you get faster access. It could be that.
Maybe I should not admit this - but if you have ever worked on a ship, like I have, you kind of intuitively know where and what things are. Such as the side doors in the theaters. Lot of theaters have a grand level with the main entrance a deck higher, so there is a 'secret entrance" that will get you right to the front row. But it isn't a secret, its just harder to find.