With Yunobo's help, you send Vah Rudania into the volcanic crater and can enter the Divine Beast.
Get a Treasure Chest
From the entrance of the dungeon, turn around so you are facing away from the door into Vah Rudania. Go straight ahead to the end of Vah Rudania's tail to find a treasure chest.
Get a Second, Third, and Fourth Treasure Chest
Go back to the entrance of the dungeon and go inside. The door will close behind you, and it will become very dark, but it will also become a normal temperature, so feel free to change your armor. In the room ahead, there are three glowing eyes. Shoot each one with an arrow. Then open the three treasure chests that they leave behind.
Get a Fifth, Sixth, and Seventh Treasure Chest
One of the chests that you just opened contained a torch. Use it on the blue flames, then use the blue flame on the torch in the corner of the room next to some bars. The bars will open.
There is a Guardian Scout in the next room. Kill it with an arrow or a Perfect Guard, then look for the orange eyeballs in this area. Shoot them all to get three more chests.
Get the Map
Light your torch with a blue flame, then use it to light an unlit torch in the wall across from the previous torch that you lit up. This will open more bars. Go through and find the Guidance Stone in the back of the area. Check on it to get the map and to open the shutters in the walls, lighting up the dungeon.
Activate the First Terminal
Go back toward the entrance. There are some metal doors on the left. Light an arrow on fire with a blue flame, then shoot the leaves on the doors. Then use the Magnesis rune to push the doors away from you, opening them. The first terminal is in the room beyond. Activate it.
Get an Eighth Treasure Chest
Light an arrow on fire with a blue flame, then shoot the leaves behind the terminal that you just activated. Open the treasure chest that falls from the ceiling.
Activate the Second Terminal
To the right of the ramp that goes up to the outside, there is a closed gate with a hole in the middle. Light another arrow on fire, then stand on the round marking in front of the gate, and shoot the flaming arrow through that hole to light up the torch beyond.
Light another arrow on fire, then go to the left and look at the ceiling to see some leaves. Shoot them to make a metal cube fall from the ceiling. Use Magnesis to move the cube near the wall of flame, then use your map to tilt the dungeon 90 degrees. Move the cube so that it is blocking the flames, then walk past the flames. Tilt the dungeon again, then activate the terminal.
Get a Ninth Treasure Chest
Equip your Flamebreaker armor (or any other armor that has Flame Guard) if you haven't already. Stand near the diagonal ceiling beam, then tilt the dungeon. Walk up the long ramp and go outside. Tilt the dungeon and climb up the ladder here. Walk onto Vah Rudania's head, shooting any Cursed Skulls that attack. Rotate the dungeon again so Vah Rudania is sideways. Then after the dungeon has finished rotating, turn to face Vah Rudania's body. From there, look for the orange eyeball down below to the left. Shoot the eyeball, then float down to the small ledge that it was on. Look at the underside of Vah Rudania's body down below and you will see a small hole in the circular structure. Float down into that hole to find a treasure chest. It contains a Silver Rupee.
Hit the crystal switch in this room to open the bars. If there is no crystal switch (due to a bug) you will need to go to the map and press X to leave the area, then warp back to Vah Rudania.
Activate the Third Terminal
From the Silver Rupee chest, leave the room after hitting the crystal switch to open the bars, then exit the small room. You will be in the main interior room of the dungeon. Rotate the dungeon. Go toward the entrance of the dungeon but don't go outside. Light your torch with a blue flame. You need to carry this flame for a while, so be careful not to run, or you will put out the fire. Stand near the diagonal ceiling beam, then tilt the dungeon. Walk up the long ramp, then when you are outside, turn left. Down below, there is an unlit torch. It can only be lit with a blue flame, not a normal one. Fall down below to stand near that torch, then tilt the dungeon and light the torch with your blue flame.
The ball inside of the ramp will roll downward. Follow the ball and go to where the ball stops. Tilt the dungeon and the ball will roll farther, but don't follow it yet. Go inside and stand at the top of the ramp, then look down below to see the third terminal. Float to it and activate it.
Activate the Fourth Terminal
Go to the base of the ramp where the ball rolled. Use Magnesis to lift the metal cube. The ball will roll into the pit down below and a gate down below will open. Float down there and activate the fourth terminal.
Get a Tenth Treasure Chest
Rotate the dungeon and stand near the diagonal ceiling beam, then rotate the dungeon again and walk up the long ramp. Go to the left and fall down to the blue flame torch. There is an orange eyeball to the left. Shoot it, then look for another eyeball hanging down from a ledge up ahead. Shoot it, then carefully walk to the treasure chest that you can see up ahead, avoiding the holes in the floor.
Activate the Fifth Terminal
Walk back toward the Divine Beast's body. You can't go any farther, so stand against the wall and rotate the dungeon. From here, you can reach the fifth and final terminal, which is nearby. Look around and use the map if you need help figuring out where it is.
Get an Eleventh Treasure Chest
The Main Control Unit is directly below you, but there is one more treasure chest in the dungeon. Look for the diagonal ceiling beam in the area below, and float down to it to find the final treasure chest.
Activate the Main Control Unit
Float down to the area below the diagonal ceiling beam, then go up the ramp to the dungeon entrance. From there, go to the top of the dungeon reach the Main Control Unit. When you activate it, the boss battle with Fireblight Ganon will begin.