As you head into the Ocean Realm, you'll notice that, like the Snow Realm earlier in the game, its Rail Map at first doesn't lead you to a lot of places: the track simply terminates at an island we need to go to first, which is the Ocean Sanctuary. When you stop there, proceed to the left from the station and then head up to the northwest. A creature called a Lobarrier will block your path, swiping you with its massive claw that it uses as a shield. Frontal attacks are useless, so hit them from behind with the Boomerang, then strike them from behind with the Sword.
Up ahead is a cave. Inside, go north and then around to the right and south, getting rid of the Lobarriers in your way, until you come across a gap with a switch orb on the other side behind some blocks you need Bomb Flowers to blow up. Pick up a Bomb Flower and place it so you can aim it across the gap near the blocks with the Whirlwind. If timed right, you should get a clear enough shot at the orb with the Boomerang, activating a bridge to cross the gap. Then go east and then north, slaying the Lobarriers, until you reach the staircase.
From where you exit the cave, go down the staircase to your left and head over to the right. You will see a red door, and it will say: "Follow the gazes of the statues. Trace their paths to open the door." But before we do, let's explore the island and check out all six statues and the directions they are facing. Then return to the door when you've figured out the paths and draw that same pattern on the door. (It resembles two diamonds almost forming an infinity symbol.) That same pattern will form on the door and it will open, allowing you access into the sanctuary.
However, when Link and Zelda enter the sanctuary, they find out that Carben isn't there. He left a note saying that he will be visiting his friends at Papuchia Village, which was the first stop we passed by on our way here. So let's get back to the train and set our course for the village.
When you arrive here, Zelda will tell you that this is the place where she summered when she was young. Of course, we're not here for a vacation, so let's proceed with finding Carben. Talk to the lady you meet near the station, and she will tell you about the Wise One who lives in the village. Then head down to the southern island where you'll see some birds with bars to your right, and among them riding one is Carben. Zelda tries to call out to him, but he seems to be in a trance or something. She will also remind you about the Wise One, suggesting that maybe she would know what to do.
So head across the bridge going north to the island that's immediately northeast of the south island, and in that house is the lady called the Wise One. She already knows your name, so after asking if you want your fortune told and you say you do, she will ask you three questions which you'll need to answer in a clear voice into the microphone:
1. Are you a boy or a girl?
2. What's your eye color?
3. And finally...what's your astrological sign?
With these answers, the Wise One will give you your fortune in a cryptic answer: "Below where the sky dwellers gather, near the lonely tree...there is a hidden sound stone that will call him." She will also add, "what you need for today is...," followed by whatever she comes up with from your answers.
What the Wise One is talking about is the tree below where the birds have gathered carrying Carben around. So go back to the south island and, standing south of the tree, play the Song of Discovery. This will bring up a rocket-shaped statue that will hum out a tune, but you won't see the colors of the notes, so you'll have to copy this by ear with the Spirit Flute to learn it. Get it right, and one of the birds will lower Carben to the ground, who will get irritated that somebody just learned the Song of Birds. He will explain that he's been talking to the birds about the places they've been. When Carben realizes what Link and Zelda want him for, he decides to return to the Ocean Sanctuary. He will wait for Link on the train, so let's get back to the train and get it rolling.
Return to the Ocean Sanctuary
With Carben on board, let us get going again to the Ocean Sanctuary. While we are traveling there, though, the Spirit Train will be attacked and boarded by Miniblin pirates. We will need to protect Carben from them, as they start to appear one at a time and then eventually up to four at a time from both sides, so slay them quickly. Eventually Carben will roll over to the right, as a creature called a Big Blin will come on board and slowly approach the elderly guy. He will make a broad swing with his club every few seconds, so get in some licks on him before he swings. Sometimes when he swings he will also include a backswing that we need to avoid. If we get knocked back by the club, quickly rub the stylus back and forth to shake it off. Eventually Bigblin will go down for the count and disappear. This means the attack is over.
Once you regain control of the train, continue your course to the Ocean Sanctuary, making sure you ease your way into stopping at the station instead of just slamming on the brakes. Carben will thank you for the ride home and will reward you with a Force Gem, an item that will come in handy later on in the game. This will also open up some new tracks in the Forest Realm.
Now that Carben is back at the sanctuary, make your way over there and talk to him. He will now lead you in a Lokomo Song that you need to play as a duet with him. This will unlock more Spirit Tracks to the Ocean Realm. He will also include a letter for us to read that will give us access to the way to the Ocean Temple, which is where we need to go next.
Getting to the Ocean Temple
With the new tracks opened and Carben's letter on hand, let's go to the three places marked on the included map where we need to go and blow the train whistle in order. Ferrus, whom we'll pass by on our way there, will tell us that this is what we need to do. These three places are beacons which need to be in our line of sight when we blow the whistle in order to light them. When all three beacons are lit, a stone fish mouth will open, bringing you down under the sea where the Ocean Temple is located, and...guess what?...there are Spirit Tracks underwater, and we can breathe while we're traveling them! How about that?
Still, the tracks down here have Ocean Octoroks swimming around them that will show up from time to time to harrass you. Your cannon now acts like a torpedo launcher, which means your shots will head straight to wherever you targeted them instead of traveling in an arc. As you get closer to the Temple, Armored Trains will also appear on the tracks to prevent you from reaching it. Watch for where these trains are headed and keep one step ahead of them to avoid them.