Who’d have thought there was an entire dungeon’s worth of passages inside this whale’s giant belly? Better start looking for that Princess…
You’ll begin inside Jabu-Jabu’s mouth. Octoroks will hop out of the water directly in front of you, and the weird hurt bubbles known as Shabom bounce aimlessly about the room. The “door” to the next “room” is blocked by some organic matter, but if you look on the ceiling you’ll see a small yellow “switch” that you can shoot with your Slingshot to unseal the door.
In the next room, you’ll walk along the edge of a deep pit. You can get back up if you fall down, but you should probably avoid having to do so. Electrified jellyfish known as Biri float around here. You can beat them in a number of ways, but you don’t have to, so just press on for now.
Through the next door you’ll run into Princess Ruto in a room full of strange holes. She’ll get huffy when you say you’re there to rescue her and turn right around into one of the pits. Follow her down and keep talking to her and eventually you’ll convince her to come with you, but there’s a catch - you have to carry her around.
Pick Ruto up and carry her through the nearby door into the next room. Here you’ll find a deep gap separating you from the passage on the other side of the chamber. Drop down into the gap and toss Ruto onto the opposite side. Stingers will rise up from the water and attack you, so defeat or avoid them and then step on the yellow floor switch to raise the water level so you can swim over to her. (You can also pick up Skulltula Token 31 while you’re here.)
Once you’ve reunited with Ruto, hit the ceiling switch either with your Slingshot or by tossing Ruto into it in order to open the next door and proceed. You’ll emerge in a water-filled room - an Octorok will hop out to shoot at you, so either avoid its rocks or repel them. There’s a passage you can dive into down below (don’t try to take Ruto with you, though) that leads to naught but a Business Scrub who will sell you something inconsequential for an absurdly high price (as usual!).
Wait awhile back at the entrance to the room and an elevator of sorts will come down to meet you. Hop on with Ruto in tow and ride it back up to the top floor. Proceed back through the north door again, this time crossing the hole-filled room and entering the door on the other side. Look out for the giant Bari that falls from the ceiling as you pass! Also make note of the pulsing green tentacle blocking one of the holes here.
This passage leads to Jabu-Jabu’s intestinal tract. Most of the passages are blocked by more of those strange tentacles and guarded by Tailpasaran, but there’s one to the far east that’s clear. Unfortunately, the door’s been sealed shut, but if you step on the nearby switch it’ll open right up. You can’t hold down the switch with your weight alone, so make sure you’re carrying Ruto when you hop onto it.
In this next room, defeat the various enemies - Stingers and Shaboms - and a chest will materialize containing the Boomerang!
Return to the intestinal tract and make a beeline over to the far west passage. There’s a blue switch here - what do you suppose that means? It’s one of those pressure-sensitive ones that needs to be held down constantly. You’ll have to use Ruto to weigh it down. She won’t like getting left behind but sometimes you have to do what is necessary and grin and bear the consequences.
Here you’ll run into a Parasitic Tentacle, the long end of one of those weird appendages you saw earlier blocking certain parts of the intestines. You need to use the Boomerang to defeat it - target it to zero in on its weaker midsection and let fly. In order to get in a good hit you have to be close enough to the tentacle that it dangles low to the ground. Beware its attacks - they can pack quite a wallop and send you flying across the room if you’re not careful. Once it’s defeated it’ll leave behind a chest containing the Dungeon Map.
It’ll also clear one of the previously-blocked passages, so return to the intestinal tract and pick up Ruto to bring her down the newly-cleared routes. The first passage on your left leads to a room where you have to fight your way past some enemies within a certain time limit to earn the Compass. The middle passage is still sealed for now, but the door down the hallway immediately to the east of it leads to another Parasitic Tentacle that when defeated will clear the way for you. Head down that hall to face the final tentacle, which will remove the blockage back in the hole-filled room.
Now that all the tentacles have been dealt with, return to the hole-filled room and fall down the hole that was previously blocked off. It’s the northmost hole, the second one on your right if you enter from the intestinal tract. You’ll land on top of a ledge with access to a west passage. From here you can also use your Boomerang to nab Skulltula Tokens 32 & 33.
Inside the west passage, you’ll find…the Zora’s Sapphire? Turns out Ruto lost it once when she was visiting Jabu-Jabu’s Belly and came looking for it only to find that Jabu-Jabu was sick. Toss her onto the platform so she can get it back - maybe she’ll let you borrow it for awhile?
Turns out the discovery is about to get cut short - the platform will rise up to the upper floor, and Ruto will apparently be subdued by some giant monster. It’s the Big Octo, and it will drop back down to your floor and attack you. It’s a relatively long battle - your first real mini-boss encounter - but if you keep on your toes you should survive.
Step on the large platform and it will rise up to the higher level. From there, enter the door to reach a room with some weird jelly-like appendages that wiggle around when you get close. You can stun them with the Boomerang to turn them into makeshift platforms so that you can jump over to the next room. It requires careful coordination and timing to make sure you stun them all at once, so try to hit one right after the other to give yourself a solid window during which to leap across the chamber.
You’ll emerge at the top of the tall shaft in the entryway to the dungeon. Leap across to the ledge on the opposite side of the room and it will slide down and settle into place, creating a way to the door at the south side of the room. There’s a blue switch here that you need to hold down to enter, and without Ruto at your side you’ll need something else. Fortunately, Jabu-Jabu seems to have swallowed some crates that you can make good use of.
In the next room, defeat or avoid the enemies and climb the “vines” up to the top of the ledge (grab Skulltula Token 34 from the far side while you’re at it). There’s a ceiling switch nestled on the other side of a web-like barrier. It’ll be tricky to hit, but if you L-target it and stand at a good distance from the barrier you can toss the Boomerang and it’ll travel in an arc and hit the switch. This opens a door leading to the boss’s chamber.
At first, Barinade is linked to the chamber’s ceiling via a set of parasitic tentacles, rather like the ones y you faced earlier. L-target them and take them out with your Boomerang to detach it from the ceiling. If you take too long, it’ll shoot lightning your way, but if you keep moving you’ll dodge its attacks pretty easily.
Once you’ve severed the tentacles, it’ll send out a swarm of five Bari which spin in a circle around it. They’re connected to the main body via electric currents, so you can’t get too close - use your Boomerang to defeat the Bari one at a time. After you defeat these first five Bari, Barinade will start moving around the room, guarded by another set of five Bari. It will start shooting lightning at you more aggressively now and you need to keep on your toes to avoid getting shocked.
Take out these five Bari and the creature’s central core will be exposed. Chase it around the room and try to hit its body with your Boomerang to stun it, then close in and strike it repeatedly with your sword. After a couple rounds Barinade will burst and Jabu-Jabu’s curse will be lifted. Princess Ruto will appear and the two of you can warp out of the dungeon together. She’ll give you the prize - Zora’s Sapphire - as thanks for rescuing her.
Ocarina of Time screenshots courtesy of AceofSuns. Screenshots will eventually be replaced with 3DS version images, which are not presently available for hopefully obvious reasons.