Your next destination is the Underwater Reactor, which you can find in Junon, but there are several side quests that you can do at this point in the game.

You can save most of the available side quests until you reach the end-game content at the end of Disc 3, but you do have the option of completing them at any point now that Cloud is back in your party:

To reiterate, many of the quests listed above can and should be saved until later in the game after you have completed most of the story—especially the Chocobo Racing and Breeding side quests, which are much easier once you have more expendable gil.

Travel back to Junon and enter the town from the side into Under Junon.

Junon

Speak to the guard standing in front of the elevator and pay him 10 gil to take you to Upper Junon, as this is now the only way to reach the city on the surface.

Walk down the streets, and the team will notice that the large cannon in Junon (Sister Ray) is no longer there.

Continue walking westward until you reach the area in the screenshot below. You will hear the sound of a whistle from some marching Shinra Guards when you get to the correct location. Walk towards them, and they will all run away.

Follow them and pass through the doorway (labeled “1”) into the elevator. You will have to fight against two Shinra Soldiers, who are listed as the “Submarine Crew” in the game.

Junon Path

Exit the elevator, and you will have to fight two more Submarine Crew soldiers. Follow the passageway. There is a Save Point in the third hallway. Ride the next elevator down into the reactor.

Underwater Reactor

Travel to the end of the hallway and then follow the pathway along. Press the red button on the far side of the elevator to reach the actual Underwater Reactor itself.

Follow the walkway along past the submarines and into the next hallway, where you will find another Save Point. Use this Save Point to save your progress, as there is an upcoming boss battle that is quite difficult.

You have a few more Shinra Soldiers to fight in the next area. You can fight the first Soldier by himself, or you can run past him, and your party will be ambushed by soldiers from both sides. The very last group of Shinra Soldiers that you fight is full of a special type of Soldier called Underwater MP Soldiers (shown in the screenshot below).

You can steal a piece of armor called Shinra Alpha from them. This armor has a strong defense against physical attacks and a mediocre defense against magic attacks, but it is worth picking up on your way through.

The Huge Materia will be carried off into the red submarine in the next screen. Walk a few steps forward to continue the story by talking to Reno. The next boss battle is against the robot standing behind him.

Carry Armor drops the God’s Hand weapon, which is an excellent weapon for Tifa.

It does not have much room for Materia, but it does have very high “Attack“ stats and “Attack %,” which means that it can never miss. This configuration makes it perfect to pair with Deathblow Materia, which will cause her attacks to either be a critical hit or miss entirely—with God’s Hand, she will have a critical hit with every attack.

Take a left before you go towards the other submarine and grab the Battle Trumpet weapon for Cait Sith out of the treasure chest at the end of the dock.

There is another treasure chest near the submarine that contains a Scimitar for Cid. This spear is one of the best weapons in the game for leveling Materia, as it has triple growth, but there is not much use for it just yet.

There is another treasure chest at the very end of the dock, containing the Leviathan Scales, which are a key item for use back in Wutai. Proceed up the stairs and do battle with the Shinra Soldiers blocking your pathway to the submarine.

Inside Submarine

Save your game at the Save Point inside the submarine and then proceed to the bridge when you are ready for the submarine battle mini-game. Click on the next button below for more information about the Submarine fight.