Otka Island

Otka Island is a visitable location in Golden Sun: Dark Dawn.

Otka Island is an island with a metallic labyrinth within a cave, hidden away amidst reefs in the middle of the Otka Sea, between Port Rago of the Morgal Region of Angara and the Nihan Islands, where Izumo was in The Lost Age and where Yamata City is in Dark Dawn.

The only way to reach Otka Island is to allow the whirlwind blowing around the Otka Sea to carry your ship to the Island. Getting back aboard the ship and sailing within the reefs around the island causes the whirlwind to come back and drop the ship somewhere north of Tonfon's port. The two things of note in the Otka Island dungeon are the Jupiter Djinni Lull, available in the first room, and the summon Catastrophe, guarded by the Ancient Devil in the depths of the labyrinth.

First Visit
The Jupiter Djinni, Lull, is at the very beginning of this Dungeon and to get to it you need Himi as well otherwise you cannot get the Djinn nor Catastrophe because you need her Search Psynergy. Also of note you can not get Catastrophe without the Sol Blade due to it acting as a key in some parts of the game. This being said, you can still get the Djinni early.

Second Visit with Sol Blade
The first 3 or 4 rooms are very easy, after that it is quite difficult, although there are quite a few treasures to find. The reason this is complicated is because there is no map whatsoever and Catastrophe is in the no map part of the dungeon.

One method of successfully traversing the dungeon is to use the "left hand rule". Which is a simple way to navigate any labyrinth. Traverse the dungeon by having Matthew's left hand always against a wall, will ensure at very least that you will always arrive back where you started. By using this rule from the second room in the labyrinth, it is possible to navigate the entire dungeon, collect all items, and find the exit (although Retreat Psynergy can be used here) without the use of a map. Equivocally, this works using either the left or right hand side, as long as Matthew never leaves contact with a wall.

Walkthrough to get all of the treasures: After using the Sol Blade on the door and climbing down the subsequent stairs into the maze, proceed north to the room with a big pit in the center, and exits to all four directions. One room above this is the Mythril Silver. Now go left one room and up four rooms to a room that branches left and right. If you want a Power Bread, go right four rooms, down four rooms, left one room, and up one room, and now backtrack down one room, right one room, up four rooms, and left four rooms to get back to this fork.

Now go left one room, up two rooms, left one room, up one room, left one room, up two rooms, right one room, up one room, right one room, up one room, and right four rooms. You should end up at a room with an elevated central portion and where your forks are right and down. To get the Triton's Ward, go down three rooms, left one room, down two rooms, left one room, and up two rooms, and now backtrack down two rooms, right one room, up two rooms, right one room, and up three rooms to return to this fork.

Go right one room, up one room, right two rooms, down one room, right one room, up one room, right one room, down two rooms, right one room, down one room, right one room, down four rooms, left one room, up one room, and left one room. You should end up at a room with an elevated central portion and where your forks are left and down. If you want a Psy Crystal, go down twice, left once, down once, left once, down once, left once, and down once, and then backtrack back to the fork. To complete the trip to the final room, go left twice and up twice. The final room contains an altar with a summon tablet; however, the moment Matthew and his group approach it, the Ancient Devil drops down from above and declares itself the Guardian of Wind. In order to claim the Catastrophe summon, the party must defeat the powerful boss of this secret dungeon. After collecting it, cast Retreat.

Collectibles

 * Triton's Ward
 * Mythril Silver
 * Power Bread
 * Psy Crystal
 * Catastrophe Summon Tablet
 * Jupiter Djinni Lull
 * Quality Zol