Trading Post

Zelda ST Walkthrough - Trading Post in Forest Realm.

Walkthrough

After obtaining Ocean Rail Map at Tower of Spirits, head southeast for Ocean Realm. The bridge to the Ocean Realm is broken and you can't drive over it.
Visit Trading Post near the broken bridge.
You'll meet Lineback Ⅲ at the office. Talk to him twice to learn about the bridge worker living in Snow Realm.
Head back for Tower of Spirits, then leave for Snow Realm.

If you successfully brought the bridge worker to Trading Post, he'll start working on the bridge after talking with Lineback Ⅲ.
Talk to Lineback Ⅲ in his office. You'll receive the letter from Lineback. Lineback Ⅲ will open the entrance to the cave that leads to his grandfather's tomb.
Go through the cave then leave by the north exit. Play the Song of light in front of the statue with a hole. You can play the Song of light by following the tones the statue emits with your Spirit Flute.
Hit the switch to the northeast of Lineback's tombstone with the Boomerang. The bridge leading to the new cave will appear.
Inside the cave, follow Lineback's instructions in the letter. You'll find the Regal Ring.
After obtaining the Regal Ring in the cave, return to Lineback Ⅲ's office. Talk to Lineback Ⅲ, then the bridge worker will take the Regal Ring for payment.
From now on, Lineback Ⅲ will do business with you. He'll offer new trains for treasures, and buy treasures that is unnecessary for you.
Head for Ocean Sanctuary in Ocean Realm.