Bring a Relicanth and Wailord to the Sealed Chamber and an earthquake should go off. This unlocks the island cave. ^_^
open
the code is open and you can get the symbols on top of the entrance of the cave
You need to know the move dive and get something from underwater
you get the sapphire stone in the 6th island you have to open the cave somehow and you get a lugia if you go to the very bottom use cut on the cave
The Golden Vase is inside the cave where the Vikings are, in 831 AD (2 o'clock on the time device). Get the barrel of gunpowder from the Great Wall of China (1593 AD) and click on the cave to open it.
open that's O P E N
To open the cave at 831 AD, get the gunpowder from the Great Wall of China.
You will see some colored numbers. Press the colors in order.
icefall cave is on 4 island and ember cave is on mt ember, northernmost of 1 island.
The cave at 831 AD is covered by rocks. Get the barrel of gunpowder from the right side of the Great Wall of China in 1593 AD. Clicking on the rocks will automatically set off the gunpowder and open the cave. (see related question)
You can find the sapphire in the dotted hole cave on six island to find the cave go to the southern portion of the island, use Cut on the door to open it then fall down the hole in the cave then fall down the holes in this sequence: up, left, right, down.
Go to four island and go in icefall cave find HM7 then use it to go up the waterfall go to the ladder then defeat the rocket talk to lorelei then leave and go to six island go back to the cave and the guy will not be there use Cut to open the door.