Start on the deck side, swim down to the lobby. Make your way across the decks into C deck, from here make your way along the deck towards the bow checking out the rows of toilets and all the artifacts.
When you reach Cargo 2 drop down and head through a hatch back into B deck, here is the sign for the ladies toilets and a typewriter among other things. Weave your way back down to the lobby and into A deck.
From here you will swim over and through bathrooms, back up and out through one of the doors onto the deck and head back to the bow.
Thanks to Victor Hawk for the video!