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 Jupiter Djinni, Lull, is at the very beginning of this dungeon. Himi is needed for her Search Psynergy. Hop right to the chest containing some Quality Zol. After, fight the Djinn as that is the only thing that can be done until the Sol Blade is obtained.
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 would be more reliable) 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 contains some Mythril Silver. Now go left one room and up four rooms to a room that branches left and right. To get some Power Bread, go right four rooms, down four rooms, left one room, and up one room. 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. 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. To get a Psy Crystal, go down twice, left once, down once, left once, down once, left once, and down once. 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, Ancient Devil will drop 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.