Ice Cavern

Age	Adult
Entry	Zora's Fountain (frozen in the adult era): go through Zora's Domain behind King Zora and walk across the ice floes to the cave
Dungeon item	Iron Boots (Iron Boots chest)
Small keys	None
Boss	None
Song	Serenade of Water (Sheik, at the end)
Gold Skulltulas	3

Bring at least one empty bottle. The cavern is full of red ice that can only be melted with Blue Fire, which you collect inside.

The first rooms have spinning blades. Collect the Silver Rupees in the spinning-scythe room to open the way on.
Scoop up Blue Fire in a bottle from the blue flames you find. Pour it on red ice to melt it. Blue Fire is refilled from the same flames, so go back for more when you need it.
Behind red ice walls you find a Piece of Heart and other treasures.
The last puzzle is a sliding ice-block room with Silver Rupees. Push the block so it slides across the slippery floor and stops where you need it, and plan each push before you make it.
Collecting all Silver Rupees opens the way to the Iron Boots. Sheik then teaches you the Serenade of Water.

Take Blue Fire to King Zora in Zora's Domain and pour it on him. He thaws and gives you the Zora Tunic.
With the Iron Boots and Zora Tunic you can enter the Water Temple at the bottom of Lake Hylia.
As an adult, the Zora Shop in Zora's Domain is sealed by red ice as well – melt it with Blue Fire to shop there (Zora Tunic: 300 Rupees).