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
icefall cave is on 4 island and ember cave is on mt ember, northernmost of 1 island.
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.
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.
the island cave is on route 105.