Back aboard the Highwind, Cait Sith lets you hear of Shinra's new plans. Apparently, they're gathering Huge Materia from various regions (as you probably remember from Gongaga reactor, if you went there). They're going to use that to blow up the Meteor. So now it's your job to rescue the Huge Materia from them. The following two sections can be done in any order.
Huge Materia in Corel
Cid heads the party now, so head back to Corel Reactor. In case you forgot, back to North Corel, up, over the big hangbridge, and follow the tracks. You really want to save the game at the save point here. If you fail here and you haven't saved, it isn't completely disastrous, but very annoying.
As you reach the door of the reactor, two soldiers stop you. They're not very tough. After you defeat them, the materia train comes from the reactor. Cid heads in and you follow the train on another train. You have 10 minutes to stop the materia train. Follow the on-screen instructions and alternate between and . Keep doing that in good rhythm and sooner or later, you reach the other train and jump in. and
In each car, you have to fight a creature or maybe even two. Summons work great here, but take too long - Enemy Skills like Beta, Trine and Magic Breath are more time effective. You need to fight five times in total, then you get to the engine, where you'll need to dispose of the soldier who runs the train. Then comes the critical part. As Cid says, you need to push the two levers in the same direction to stop the train. The left lever is controlled with and (up and down), and the right lever is controlled with and and (up and down). To stop the train, alternate between pressing and + and +.+ and + . You can also use instead of .
If you manage to stop the train, a kid will give you Ultima materia and you can find the Catastrophe (Barret's lv4 limit break manual) from a woman in one of the huts. If you fail, you can still buy the Ultima materia from the kid, it just costs a lot. If you fail to reach the materia train at all, you won't get anything.
Huge Materia in Fort Condor
The second Huge Materia is at Fort Condor. Instructions for beating that minigame are in a separate article.
This time is a little bit different: the condor will die in a giant fireball and the egg hatches. After the battle, head through the door to the top of the reactor, and you see the newly hatched bird, along with a red orb, the Phoenix materia. Then talk to the folks at the fort, especially the warboss' father who sits by the table downstairs. He'll give you the Huge Materia.
Return to Mideel
As you return to Mideel, things seem to be a bit more tumultuous than before. The ground starts shaking all of the sudden, and it seems the Lifestream is very, very upset. Suddenly, a big dragon-like creature appears out of blue and you are forced to fight it.
In the following cutscene, the town gets destroyed, and Tifa and Cloud drop into the Lifestream. A long cutscene follows, after which it is finally time for Tifa to help Cloud come to grips with who he really is. You'll find out a lot of information about what really happened in Nibelheim, for instance. The only thing you need to do is run around as Tifa and talk to Cloud occasionally. After a bit of rest, Cloud goes back to leading the crew.