This room houses the mark of Nayru, which Fi point out to you. Anyhow, defeat the Electro Spume in the quicksand nearby, then dash across to the hill, atop which you’ll find the Timeshift Orb.
Grab the Timeshift Orb and hit the ground. Since the quicksand becomes grass and all that, work your way to the other side of the room, where you’ll find a differently-designed tile. Place down the Timeshift Orb there.
Go to the top of the hill on the other side of the room and stand onto the platform. On the far high ledge, you can find an eye switch across the room – hit it with an arrow, which lowers the bars to the left of the Timeshift Orb. Go back to and grab the Timeshift Orb, then go through the newly-opened doorway.
Here, go along the path, defeating the Deku Babas and Quadro Baba as you do. Now, at the end of the path, we need to drop the Timeshift Orb somewhere where the platform you saw on the way is not raised, and the fan at the end is not blowing. An easy place is the corner nearby.
Next, stand in front of the fan. Shoot an Arrow through the fan to the eye switch on the other side, which can only be seen if you’re on the floor switch (which you probably already are).
Afterwards, grab the Timeshift Orb and go underneath the ledge on the east side of the room. Defeat the Technoblins there. Drop the Timeshift Orb so that the platforms nearest the ledge have risen.
Dash across the quicksand and go up the hill nearby. Get onto the platforms and Clawshot towards the ledge, then go into the room nearby. Thrust your sword into the alternate realm.
Here, grab the Triforce of Wisdom, completing the Triforce. After a few scenes, you’ll end up back in the Sealed Temple on the surface. We’ll continue into the next section.