Back on Mercay Island, the shipyard has opened by the docks. Here, Link can swap out parts of the ship to upgrade Linebeck’s ship. There’s a treasure chest here with a part so he can try it out. Using multiple parts from a set upgrades the ship’s stamina, so maybe for now Link may as well stay with Linebeck’s default parts. There’s not much else to do, so it’s time to check out the Temple of the Ocean King again. As Link enters, Linebeck comes in behind him, warning him that if he goes in unprotected, he’ll end up like the skeletons lying around the entrance. He tries to scoot off to leave Link to explore the temple, prompting yet another argument between him and Ciela [1], and it’s like okay, game, I get it already, he’s a coward and she doesn’t like that very much.
Oshus shows up to spare the player too much arguing, and says Link’s impressed him by freeing the spirit of power and might have a chance against the ghost ship after all. He points to an altar near the entrance deeper into the temple, where an hourglass sits. As Link approaches, the altar explodes with sand. At Oshus’ direction, Link takes the hourglass and the sand pours into it. It’s the Phantom Hourglass, which can protect Link from the Temple’s energy drain as long as it has sand in the top. (Linebeck brings up the idea of flipping it back over, but it’s magic sand and being drained depletes the magic until it’s restored. Going outside restores the magic, but also resets progress.) Defeating certain monsters, like Blaaz, gives Link more sand, and thus more time. Linebeck asks Oshus how he knows so much, but Oshus says he’s not ready to reveal all his secrets, because of course he’s not.
The first floor, that Link explored before, is mostly bypassed this time: the way forward isn’t blocked, and Leaf can open the door leading deeper into the dungeon. The next floor is patrolled by armored enemies called Phantoms, which Link can’t fight. So, stealth mission it is, although unlike many other stealth missions in the series, being spotted isn’t an instant fail. If Link can get to a safe zone before he’s caught, the Phantoms won’t be able to get to him, and they’re not smart enough to camp the zone waiting for him to come out so they can grab him. Small mercies; combining a stealth mission and timed mission is approximately like combining a vision test with a blindfold. (The Phantoms can also hear noises Link makes like breaking pots, but still can’t get into safe areas.)
This trip through the temple requires passing through three floors. The first two are basically Link sneaking around doing dungeony things to get a key to open the door forward. The third floor is a lot more complex: Link has to gather three gems to place into sockets to open the way forward. One of the gems is behind a locked door, and the key held by a Phantom (a helpful skeleton/ghost/hint dispenser tells Link this in case the player doesn’t notice the doubled-up icon on the minimap), so Link needs to dispose of the the Phantom by waiting till it walks over a trap door and then sending it falling to its doom. In addition to normal pots, there are two special kinds of pots to help Link advance: red pots create small safe zones where they break, and yellow pots restore some time to the Phantom Hourglass.
After the three puzzles are past, Link comes to a safe floor. His life doesn’t drain, and there are no Phantoms, so he can just head over to the treasure chest with the next part of the sea map and claim it. Once he does, a portal leading to the surface opens, and armed with what he came for, Link heads through. Back at the seaport, he finds Linebeck minding the ship. The map’s covered in dust, making it hard to read, so Link gets to blow the dust off the map, which of course is the player blowing into the microphone again. The cleared map has an island marked with Nayru’s symbol, so that’s where the Spirit of Wisdom probably is, and Link’s next major destination.
Next: Getting armed for the journey.
[1] I just realized that even though I don’t think I’ve misspelled her name, I’ve been reading it wrong (as “Celia”) and probably saying it wrong in my head.