Instructions
Walk into the large area with eight statues. Go up to the statue that makes noise and watch the cut scene.
Load the picture of the overhead map to view the eight statues. Use the stylus to draw a line from the top left corner statue down to the bottom right statue. The statues will spin and face each other. The door will open for Zelda to go through.
Walk through the door and approach Gage, who is a spirit. He will play a song on his flute.
Press on the orange, yellow and purple musical notes to match Gage's song. Perform it in the same rhythm to match the song. Once you do each note, blow into the microphone to play it back on the flute.
Watch the rail map glow after you duet with Gage. A path will open up for the train to reach the Forest Temple.
Blow the train whistle to scare off the Skulltula spider creatures that try to jump on the train. Once you get past the spiders, the temple door will open and the train will enter.