Fuchin Falls Cave

Fuchin Falls Cave is a dungeon-style location in Golden Sun, which is connected to Fuchin Temple on the east end of the continent Angara. It is blocked by a man by order of the temple's head monk, Master Nyunpa, and it is a test of Psynergy powers, which Nyunpa teaches as "Ki" spiritual power. Nyunpa will grant Adepts with Psynergy access into the cave. The cave itself includes puzzles involving rolling logs and using a key item called the Dragon's Eye on a dragon statue to light up a room and reveal the shadows of an otherwise invisible path, and among its treasures are the Arctic Blade and the utility Psynergy item, the Orb of Force.

This is actually an optional dungeon that can be skipped, and the Orb of Force is not required to reach the game's end. The Orb of Force is required to get to some major secrets both in this game and in Golden Sun: The Lost Age, however.

Walkthrough
This is the test you must undergo. Compared to Mercury Lighthouse, though, it's a breeze. First, read the stone in the center of the room. Then, pick a log that's in the water, either left or right; the left lets you go on, while the right leads to a mimic. Once you've gone up the left side, walk north through a door. In the next room, walk to the edge of the water, in front of the platform in it that isn't touching the shore, and then jump on. Jump right twice, then north twice. Go right, then north until you are on a platform that's against the north wall. Take the left route, ignoring the center door and once you reach the left wall, head south and go up the stairs into the next room.

In the next room, there are three doors on different levels. Go straight north through the one on your level into a dark room. In here is a set of stairs that leads down. This room is lit once more; there is a log in the water that moves south, and a little further down is one that goes to the left. Take the left one to reach a treasure chest containing the Arctic Blade, a fairly powerful sword. Once you've grabbed it, head back to the right and then take the south moving log. Go through the door on the other side. In this room, there are many spikes on the floor. If you step on them, you'll take minor damage; you can just walk right across them if you want, or you can't afford to take any damage, follow the leftmost path to a log in the water which will let you bypass the spikes entirely. After you have gotten past the spikes, there's a door on the right side. It leads back to the first room, but this time from a different angle. Get on the right moving log and enter the door on the opposite shore. This room has a large mass of spikes and, to the south, a wide body of water with several logs. On the right shore, there's a Jupiter Djinni; to reach it, move the log south, then walk onto a vertical log to roll it against the wall. Take the original log back to the north, then jump to a platform in the left corner, and south onto the vertical log you just moved. Roll it to the right and engage the Djinni in battle. Once it is defeated, Zephyr will be added to your collection. Head south along this right-side shore and take the horizontal log at the bottom up north. Go through the door that's on the other side of the spikes.

In this room are many logs and platforms; you need to organize them into a pattern that will allow you to reach the down stairs on the left shore. To do this, move across the double logs and roll one up north. Walk on to the land, and then around to the right shore. Roll this log to the left, then jump north onto the first log. Walk back around to the southern shore and roll the second of the double logs up into the one now resting against the left wall. Jump onto the left shore and go down the stairs. In this room is the Dragon's Eye. Take it and go back up the stairs. Now head north across your log bridge through the upward staircase. Go through one more door in this room to reach the darkened room. This time, climb up and you will see a dragon statue. Talk to it, and place the Dragon's Eye in the socket. It will shoot forth flames and reveal a formerly invisible path. Go back through the previous room, down the stairs, and walk all the way to the entrance to the first room referenced in this paragraph. Take the log on the right shore of a small pond onto the opposite side, and enter the door. You will now be back in the second room of the dungeon. Jump across all the platforms to the left side shore again and ascend the stairs. Walk north through the three-doored room and into the (formerly) dark one. You will see the shadow of a path has been revealed on the floor. Walk carefully along it, and you will end up on the northern right door. Move through, up and around the wall to a dropoff point. Slide down and enter the door. In this room is your objective; before talking to the stone, grab the chest next to it to get the Orb of Force, an item which grants the user the ability to cast the Psynergy Force. This an outside of battle only skill, much like Catch and Move. Now, use Isaac's convenient Retreat skill to exit the dungeon.

Items
Arctic Blade - In a chest in the second room.

Orb of Force - At the end of the invisible path.

Djinn
Zephyr - In a log-rolling puzzle south of a large mass of spikes.