You'll be in the water at the beginning of this chapter, so dive down. Look to the back and right for a cave entrance, then swim to the top to find a ledge with a Phoenix Feather and Gorgon Eye. Now, get back in the water and swim all the way to the end, surfacing and being forced into a fight with two Ice Talos.
At first, you only fight one of them, and they are pretty easy, as they either swing their hammer side to side, or smash it down in front of them twice, creating some ice spikes similar to Plume of Poseidon (Ice of Poseidon attack). Whenever you see them encase themselves in ice, stop attacking until they get rid of it, then continue wailing on them.
Once they're dead, target the giant chains on both sides of the room with your Amulet and decay them to open the door ahead. Jump into the water and swim through the path until you get to a sidescrolling section. When you get the chance to go down, do that and you'll find the Boat Captain's Idol Artifact glowing on the ground, so grab it and swim the rest of the way until you can go back on land.
In this section, go to the right to find some Red Orb Chests, then go all the way to the left to find a Phoenix Feather and Gorgon Eye. Board the ship to view a cutscene that will take you to the next chapter.
