One big story arc of “Final Fantasy VII” is the quest for Huge Materia during disk 2. The party must stop Shinra from obtaining such power, as they wish to use it to combat Meteor, the giant imposing asteroid threatening the world. However, in using such power, the Plant's life force would be drained and the power wouldn't even be enough to stop Meteor.
The payer will obtain one of two Huge Materia with the natural progression of the story, however it is possibly to obtain each and every Huge Materia, and each give quite the reward if one is willing to put the required time into it. The first Huge Materia to obtain is from the reactor at Mt. Corel. Upon arriving at the reactor, a Shinra train can be seen leaving the area with the Huge Materia.
The party then obtains a train of their own and begin chasing down the renegade Materia carrier, which is on a crash course straight to the small mountain settlement of Corel. After catching up, the party must fight through five carts, each containing one battle, and then stop the train. If the train is caught up to, commandeered and stopped within 10 minutes, then the Huge Materia is obtained. Otherwise, it is lost forever.
Next, the player may head to Fort Condor and complete a small mini game to defend the reactor from Shinra forces. Upon successfully defending the area, an old man within the fort will provide the party with Huge Materia that he took from the reactor, incase Shinra broke through. After this, the story will lead the heroes to below Junon, to it's Underwater Reactor. After advancing through the area and defeating the boss, the party will take control of a submarine and attempt to shoot down an enemy sub carrying Huge Materia. After destroying the enemy vessel, the player will be back in the overworld. One must then dive under water in the submarine and search for the remains of the enemy sub, where the Huge Materia can be found.