To free Vah Nabooris, you must seek the leader of Gerudo Town.
Go to Gerudo Desert
If you want to ride a horse to Gerudo Desert, first go to Rota Ooh Shrine and take your horse out of the nearby Outskirt Stable. (Or if you don't have a horse, go east of Rota Ooh Shrine and catch a horse in the hills north of Great Plateau.)
Then go south on the road that goes past Outskirt Stable, then at the fork in the road, go west.
You will go across Digdogg Suspension Bridge, which has a Hinox in the middle. On horseback, you can just gallop past it. On foot, you can outrun the Hinox. Or you can battle it if you choose.
South of the Digdogg Suspension Bridge, the road will go past Jee Noh Shrine.
From Jee Noh Shrine, continue on the path, that goes northwest. Watch out for falling rocks. Eventually the path will be blocked by some boulders. Use Magnesis to pull and push the metallic boulder through the other boulders, clearing the path.
Continue riding your horse along the path and you will reach Gerudo Canyon Stable. Board your horse there, because you can't ride a horse in the desert.
There is a shrine on the cliff across from the stable. It is the Kay Noh Shrine. To reach it, you can either climb the cliff, or climb the tall rock spire in front of the stable (lifting the rock at the top to find a Korok) or you can walk east from the stable and walk up the slope to get to the top of the cliff.
From the Kay Noh Shrine, you can reach the Wasteland Tower.
Protect Yourself from Heat and Cold
Now warp back to Kay Noh Shrine. Before you enter Gerudo Desert, you will need protection from heat and from cold.
For cold protection, you can buy Warm Darners from a merchant near the stable, or you can just wear the Warm Doublet that you can get in the Great Plateau, or go to Great Plateau and get Spicy Peppers.
For protection from heat, you can buy Cold Darners and Winterwing Butterflies from Beedle and cook one of those with monster parts to make heat-resistance elixirs (Cold Darners create elixirs with a stronger heat-resistance effect).
Another option is to equip a Frost weapon during the day and a Flame weapon at night, if you have any.
You could also go gather the following food ingredients to make food with heat-resistance effects.
- Hydromelon can be found in Faron Grasslands or Gerudo Desert for low heat-resistance effect
- Cool Safflina can be found in Hebra Mountains or Gerudo Highlands for low heat-resistance effect
- Chillfin Trout can be purchased in Zora's Domain or gathered in Tabantha Frontier or Hebra Mountains for high heat-resistance effect
- Chillshroom can be found in Eldin Canyon or Gerudo Highlands for high heat-resistance effect
After you have some heat and cold protection, go west from the stable to enter Gerudo Desert.
Go southwest along the path through the desert. Eventually there will be a cut scene where you see the Divine Beast of this area. After that, go toward the buildings. You will reach Kara Kara Bazaar. You can buy Hydromelons here, which you can cook to make heat-resistance foods.
There isn't much else that you can do at Kara Kara Bazaar right now, so just go southwest to Gerudo Town for now. If you try to go in, you will be stopped at the door, because only women are allowed. For now, go to the Daqo Chisay Shrine next to Gerudo Town.
Getting into Gerudo Town
Outside, find Benja between the shrine and the entrance of Gerudo Town. Talk to him to hear rumors of a man who was able to sneak into Gerudo Town.
Your next destination is Kara Kara Bazaar, which you can reach more quickly if you sneak up to a Sand Seal in front of Gerudo Town. You need to equip a shield (choose a shield that you don't mind damaging a little) then when you are close to the Sand Seal, press A to grab it and surf on the sand.
In Kara Kara Bazaar, if you ask around, you will find out about a suspicious vai merchant who hangs out on top of the inn of Kara Kara Bazaar. There is a ladder on the wall of the inn. Climb up it and make your way to the roof, then talk to the merchant there. Answer the first question however you want, then say "you're very beautiful!" Then pay 600 rupees for a vai outfit.
After the cut scene, warp to Daqo Chisay Shrine and enter Gerudo Town. The guards will not stop you. But be careful not to change your armor while you are in town, or you will be spotted immediately and thrown out.
Talk to Riju
If you keep going straight from the entrance of Gerudo Town, you will reach the palace. Go inside and there will be a cut scene where you talk to Riju. She asks you to retrieve the stolen Thunder Helm. She tells you to ask Captain Teake for more information.
Leave the palace through the north exit that Buliara showed you. In the northern corner of town, you will find Captain Teake. Talk to her to learn the location of the Yiga Clan's hideout: Karusa Valley. The location will be marked on your map if you select the Divine Beast Vah Nabooris quest in the Adventure Log.
Get the Thunder Helm
Stealth armor will help in the next part of the game. You can buy it in Kakariko Village.
Be aware that as soon as you encounter your first Yiga in the game, from then on you will encounter them randomly in some regions of Hyrule. If you don't want to battle any Yiga while you travel around, wait until later to complete this Divine Beast quest, and don't talk to travelers who try to get your attention on the open road, because many of them are secretly Yiga.
If you are ready, go northwest from Gerudo Town. If you encounter a sandstorm, you have gone too far west, so go back east.
In Karusa Valley, watch out for falling rocks. Yiga Footsoldiers will attack as you make your way to the Yiga Clan Hideout.
Yiga Clan Hideout
Inside the hideout, burn down the wall scrolls. There is a torch leaning against the podium in the center that you can use, or you can shoot fire arrows, or light regular arrows on fire with torches, or use Flame weapons. You will find some treasure chests behind the wall scrolls, but also some Keese that will attack.
One of the hidden passages has stairs going farther into the hideout. Up ahead, you will find Barta, a Gerudo who was captured. Take the Mighty Bananas from outside of her cell.
Equip Stealth armor if you have any. Go down the stairs near Barta's cell. Then slowly go into the hideout area. There is a Yiga Blademaster patrolling the area. You need to go past the fence on the other side of the room. Do so without letting the Yiga see you.
There is a short flight of stairs beyond that fence. Stand here and shoot the small red X on the piece of wood that is holding up a shelf. This will make some Mighty Bananas fall on the ground. The Yiga nearby will slowly go over to the bananas to pick them up. While the Yiga is distracted, go through the door that he was guarding.
In the next area, you will see a ladder up ahead, but there is also a door on the right. The ladder leads to an upper area where you can get a lot of Mighty Bananas and a chest.
There are several Yiga patrols in the area, so you will need to be especially stealthy. There are treasure chests in the area, but you will be able to come back later when there are no enemies, so don't get the treasure chests now unless you really want to.
If you go through the door before the ladder, you can look to the right to see three wall scrolls. Shoot the middle one with a fire arrow to burn it and reveal a hidden passage. Then stealthily go around to the hidden passage and go inside, opening the two chests. Then go to the hole in the wall of the hidden area and jump over the spikes. Go up the ladder at the end and you will be above the exit of this area. Stand on the roof and hold a Mighty Banana, then press down on the directional pad to change your aim to throw the banana far away. Press A to throw it. The Yiga below will go over to it, giving you a chance to fall straight down and go through the door he was guarding.
There are other ways to get through this area, but the above is one of the easiest.
The next area seems like a dead end, but use Magnesis to rotate a secret metallic wall. Before you go through, be sure to get the treasure chests buried in the dirt. There will be a boss battle after you go through the hidden door.
Kohga will protect himself behind force fields, and will create large boulders that he will throw at you. Shoot Kohga with an arrow when the boulders are above his head to make the boulder fall on him. Then attack him until he gets up.
Eventually he will float above the pit in the ground and make a couple of boulders spin around him. Once again, shoot him when a boulder is over his head, and the boulder will fall on him. Run over to him and attack him until he gets up.
Next, he will create a spiked metallic ball and start throwing it at you. Use Magnesis to hit him with the ball. Repeat this until Kohga is defeated.
Open the treasure chest that appears, and you will get the Thunder Helm.
The hideout is empty now, so explore it if you wish.
Return the Helm
Go back to Gerudo Town, equip your Gerudo vai armor so the guards won't throw you out, and talk to Riju. She is upstairs from the throne room now. There will be a cut scene when you talk to her. She says that she will wait for you at the Lookout Post south of Gerudo Town.
Reach Vah Nabooris
Equip a shield that you don't mind damaging, then sneak up on a Sand Seal outside of Gerudo Town. Or you can rent a seal for 20 rupees in Gerudo Town.
Ride the seal to the Lookout Post south of Gerudo Town, then go around the side of the building and go up the ladder to find Riju at the top. Tell her if you are ready. If so, she will give you 20 Bomb Arrows that you will need to use on Vah Nabooris. If you are ready to proceed, say so, and you will go to Vah Nabooris.
Before you reach Vah Nabooris, just stay within Riju's protective circle. There will be a cut scene when you get close enough to the beast to start shooting.
After that cut scene, if you see a reticle on you, move into the protective circle around Riju and wait for the lightning to strike. You need to be careful not to go too quickly or too slowly to keep up with Riju's pace.
If you have a Duplex Bow, equip it to do double damage. Each foot needs to be hit twice, but the Duplex Bow will hit twice with one shot.
As soon as the lightning strikes, dash close to Vah Nabooris's feet, and shoot them with bomb arrows while you are close. If you try shooting from far away, there is too much risk of missing the shot and running out of bomb arrows, and it is also pretty difficult to both steer and aim from a distance.
After you disable all four feet, there will be a cut scene, and you will enter Vah Nabooris, registering it as a travel gate on your map.