Ice Cavern & Water Temple

The water sage

Chapter 13 of 16 of the Ocarina of Time remake walkthrough, played as Adult Link, in 8 steps.

Zora's Domain is frozen. The Ice Cavern at Zora's Fountain holds the Iron Boots; the Water Temple is the game's hardest puzzle box.

Reach Zora's Domain (climb the frozen waterfall or Hookshot). King Zora is frozen in red ice; continue to Zora's Fountain and enter the Ice Cavern.
Ice Cavern: collect Blue Fire in a bottle, melt the red ice blocking doors, push the ice blocks, and defeat the White Wolfos for the Iron Boots. Sheik teaches the Serenade of Water.
Melt King Zora with Blue Fire for the Zora Tunic (or buy it). Warp to Lake Hylia and sink with the Iron Boots to the temple entrance.
Water Temple: three water levels, changed by playing Zelda's Lullaby at the Triforce marks (low: basement, mid: ground, high: top). Collect every Small Key; there is one you can miss under the central tower at mid level. Tip: If you are stuck with no keys, the missed one is behind the block puzzle in the room reached from the mid-level central pillar (3DS marks this door).
Defeat Dark Link in the mirrored room (Din's Fire or the Hammer make it easy) for the Longshot.
Use the Longshot in the river room and under the whirlpools to reach the Boss Key, then raise the water to the top for the boss door.
Boss: Morpha. Longshot its nucleus out of the water and slash. Stand in a corner to avoid being thrown. Water Medallion.
Lake Hylia refills. Stand on the island pedestal at sunrise and shoot the sun for Fire Arrows.