This part will get you through repairing the bridge to the Ocean Realm.
Getting to the Ocean Realm
Talk to Anjean after you've gotten the Ocean Rail Map, and she'll tell you that your next goal is to talk to Carben in the Ocean Realm in order to reach the Ocean Temple. Since we have the new track opened to us in the Forest Realm that will take us there, let us get the Spirit Train rolling again. Again watch out for the Dark Trains patrolling the tracks as well as the usual land dangers. Along the route we will see another archway that will come into play as the game progresses.
Uh oh! The bridge is broken!
As we get close to the bridge that crosses over the river between the Forest Realm and the Ocean Realm, however, pull on the brakes and pull over to the nearest station called the Trading Post, because the bridge has been sealed off. As soon as you get off the train, head over to the right, and Link and Zelda will see that the bridge is a complete mess, so we can't cross it as of yet. Zelda suggests that maybe someone here at this location can fix it for us. Since there's only one house at the Trading Post, let's head there and find out who lives here so we can get the bridge fixed.
As the walkway turns, go down and then left toward the house and enter. Inside is a shop, and it's run by a familiar friendly face we've seen in Phantom Hourglass -- it's Linebeck! Actually, it's his grandson Linebeck III, but he has the same charming personality of his forebear. He runs Linebeck Trading, which deals in buying and selling rare antiques, and he will explain that the storms had caused the bridge to be in disrepair. He was going to call the bridge worker in the Snow Realm to come fix the mess, but with the Spirit Tracks vanishing, he has other things in mind. He now has us go and fetch the bridge worker since Link is a train engineer now, which would solve not only our problems but also Linebeck III's.
(By this point in the game, you should also receive a message from Russell the captain of the guard sent by the postman, challenging you to a fight with more experienced swordsmen. This part is completely optional: travel back to Castle Town and go into the guards' room in the castle where you'll need to pay a fee for a contest where you need to hit three guards at least 100 times without getting hit three times. Your reward for succeeding is a Heart Container.)
Our first passenger
Now it's time to get the bridge worker. Leave the shop and head back to the train, then plot a course back to the Tower of Spirits since our getting to the Snow Realm will now require having to go through the tower. When we get off there, have Anjean rotate the tracks in order for us to travel to the Snow Realm so we can continue.
Along the route back into the Snow Realm, pull over at the first station we see coming up. This is the bridge worker's home, and since there's only one house at this location, we'll surely find him. Follow along the walkway, slaying whatever crows and Red Chuchus happen to be in your way, until you reach the door of the house. Enter and talk to the bridge worker about fixing the bridge until he agrees to come with you. He'll meet us at the train, so leave the house and head back there. Before you get on the train, Ferrus will meet you at the station, telling you that the bridge worker is a "super-mega fussy" guy and that we're going to need to pay attention to the signs along the tracks and make sure we don't get hit by enemies or slam on the brakes suddenly. Up to now we haven't paid any attention to the signs because we haven't had a passenger to carry around, but since we want a safe and happy bridge worker doing the work we want done, we might as well do as Ferrus warns us to do.
As we carry our first passenger on board the Spirit Train, the mood of the passenger will be indicated by the color of the smiley face on the passenger car. Green means he's happy and pleased, yellow mean's he's getting somewhat irritated, and red means you might as well turn in your engineer's cap and rescue Zelda another way!
Plot a course back along the same route to the Tower of Spirits, being ever mindful of the dangers, the signs, and of course our passenger's mood. When you stop there, have Anjean rotate the tracks so we can travel through the Forest Realm again. Then plot a course to take us to the Trading Post before the bridge, watching out again for the signs as well as the Dark Trains and other assorted hazards. Bring the train to a slow crawl in order to stop it before the stop sign when you reach the station. If all goes well, the bridge worker will compliment Link on the ride putting him in a working mood.
Searching for the Regal Ring
Go into to the shop and talk to Linebeck III, who will be pleased that Link brought along the bridge worker. Go back outside and talk to the bridge worker, who will inspect the bridge and say that it's not beyond repair but it will take some time. Linebeck III will come out to talk to the bridge worker, and the worker will give the trader a repair fee of 5000 rupees, which also includes an unpaid repair bill on the house. Of course, Linebeck III declares that Link will pay for the bill since he's the one who wants the bridge repaired. The bridge worker doesn't seem to care who pays the bill, as long as he gets paid for his work when he's done.
Since we don't even have that much money in our pockets, Zelda suggests that we go give that Linebeck III a piece of our minds. Go back to the shop to talk to the old scoundrel, and he will tell us about a job we can do to cover both his hide and ours: he wants us to search for a precious item called the Regal Ring, which his grandfather left a letter about its location before his passing. Agree to do the job, and Linebeck III will give us the letter we can read to help us find it. He will tell us that the ring is located somewhere near his grandfather's grave.
So now let's start our search for the ring. After leaving the house, go west until you are south of a cave entrance. Go in and head north to the stairs, watching out for the Like Likes that will suck you into their maw and chew on you before spitting you out; if you get caught in one, do a quick rub with the stylus to break free. When you leave the cave, head to the right and you'll see both a grave marker and a rocket-shaped statue humming out a tune. Get out the Spirit Flute and copy the tune that the statue hums. You've just learned the Song of Light, and as the statue launches into the air, it leaves in its place a diamond that emits a beam of light. Follow where that beam of light is pointing to with your Boomerang, and you'll see that it's hitting a switch orb. Hit the orb with the Boomerang, and a bridge on your right will appear across the water over to an island. Across the bridge on the island is a crack in the wall we need to bomb, so grab a Bomb Flower and use it to blow a hole into a cave we can enter.
In the room that we enter, there are two light-emitting diamonds as well as some Octoroks and a treasure chest that a Like Like is using as a disguise, so avoid that chest at all costs. Slay all the Octoroks in the room. Then use the newly-discovered Song of Light at each of the diamonds to make them project their light beams, and as they project the beams, they will cross at the spot where Linebeck's letter says we should start from. From that spot, go four steps (tiles) north and six steps west, and then play the Song of Discovery. A treasure chest will pop up, and in it is the Regal Ring.
Now that we got the treasure, let's return to Linebeck III and get the debt he stuck us with paid off. He will assess the ring and say that it must be worth 8000 rupees. Soon the bridge worker will show up and say that the bridge is all patched up, and he will take the ring as payment. Despite Linebeck III's disappointment of not making a profit from the ring, he is still impressed with our talent for sniffing out treasure and that he will now reward us for whatever treasure we happen to find. That means more money in our pockets (Link can hold up to 9999 rupees), and with those rupees we can eventually buy the Golden Train set, which will give us more train hearts to travel through New Hyrule and beyond with.
So with the bridge repaired and our debt paid off, we can proceed onward to the Ocean Realm.