To get to the island, head out to Batallia Downs and go to I-10 inside the small cave and enter Eldieme Necropolis. Once inside, sneak to J-8, then go South to I-9.
One person should go to H-9, where they will be standing in front of Shiva's Gate.
If this gate is already open, walk inside and turn immediately south. This is Titan's Gate, and it should be closed.
The person still standing at I-9 must proceed North to I-8. Invisible and proceed to H-8. There is a Bomb type mob here, who detects by sight and magic, so do not cast anything around him, and make sure you are invisible before going to H-8. Pass by the bomb into another small room, and you will see a switch. Take invisible off, and then hit the switch. Now Shiva's Gate will open.
Have the person at H-9 walk through and face South toward Titan's Gate, then hit the switch again, so that Shiva's Gate closes, and Titan's Gate opens.
If Shiva's Gate was already open, you only have to hit the switch once to open Titan's Gate.
Now the person near the switch needs to put invisible back on, and head down to H-9, near Shiva's Gate. Meanwhile the person who just went through Titan's Gate will proceed to G-9. In front of them will be a room with 9 Grave Pits in it, along with a few mobs.
Do not walk on the Grave Pits themselves as they are actually invisible holes that will drop you down to a lower level of caves.
To let the other person through, proceed north to G-8 in a small room. There is another switch you must hit to open and close the doors again, letting your partner in.
Once you are with your partner again, go back to G-9 with the 9 Grave Pits, go directly to the grave pit in the middle, and stand in the middle of it. You will then fall to a cave-like area, and you will be on a different map at L-12.
Head East into another map and you will now appear at G-7.