I'm lost. I completed a voyage to unlock the Siren's Shell island. Since unlocking sirens as crew was a separate icon next to the island, I have to assume I can visit it, like I can the Cyclops' island. I am not able to change the map away from The Arc, however. How do I go to the new island, or have I misunderstood (dare I say, was it misleading)? I've read the wiki but didn't find a clear answer. It doesn't tell me how to travel to Siren's Shell but it also doesn't tell me how to visit other islands in The Arc which I can visit..