Inside Jabu-Jabu's Belly

Age	Child
Entry	Show Ruto's Letter to King Zora, then offer a fish in a bottle to Lord Jabu-Jabu in Zora's Fountain
Dungeon item	Boomerang (Boomerang chest)
Small keys	None
Mini-boss	Bigocto
Boss	Barinade
Reward	Zora's Sapphire and a Heart Container
Gold Skulltulas	4

Win the Silver Scale in the diving game in Zora's Domain.
Dive to the bottom of Lake Hylia for the bottle containing Ruto's Letter.
Show the letter to King Zora; he moves aside and you keep the bottle.
Catch a fish in the bottle (Zora's Domain has some) and release it in front of Jabu-Jabu in Zora's Fountain. He swallows you.

You need a ranged item from the start: the Slingshot is used on switches and enemies throughout the dungeon.
Find Princess Ruto early on. Pick her up and carry her with you – she has to come along for you to make progress.
Get the Boomerang from its chest. It stuns enemies, grabs items from a distance and is the item you need to destroy the Parasitic Tentacles found in several rooms.
Bigocto is the mini-boss; its weak spot is its back.
Defeating Bigocto lowers part of the floor in the main area, opening the way toward the boss.

Barinade hangs from the ceiling by three tentacles. Cut them with the Boomerang.
It then detaches and is surrounded by electric jellyfish. Use the Boomerang to stun Barinade and knock the jellyfish away, and attack the jellyfish while they are stunned.
Once the jellyfish are gone, stun Barinade with the Boomerang and slash it with your sword. Keep moving to avoid its electric beams.

Electric enemies shock you if you hit them with your sword while they are charged – use the Boomerang or Slingshot on them instead.
Ruto can be put down and picked up again at any time.