The Sewers and The Train Graveyard
Item:
Potion, "Setal"Materia, Hi-Potion, Echo Screen, Ether
Corneo's trap door deposits the team deep in the sewer system below his mansion. Take a moment to equip Tifa with any new weapons and armor you may have purchased, and give Cloud a Materia crystal or two. Also, consider equipping Aeris with the "Fire" Materia before proceeding. However, before the team can fully recover, they get attacked by the Don's hero disposal system, the giant creature known as "Aps".
Boss Fight: Aps
Aps is a strange creature. Its strongest attack is the Sewer Tsunami, a water-based attack that causes damage to your entire party. What's interesting about this attack is that it also causes damage to Aps as well. You'll notice that the wave comes from two directions. When coming from behind Aps, it causes more damage to Aps than it causes to the team. If it starts behind the team, it inflicts considerably more damage to the team than to Aps. Regardless, you may find that Aps causes more damage to itself than you can cause to it.
Aps has a definite weakness to Fire, so have your characters equipped with the "Fire"Materia. It's best to equip it with Aeris, because you can concentrate on casting to Fire spell and healing the party. The other two party members should use normal attacks, magic, and Limit Break to knock Aps into submission. If Cloud has his Cross-Slash Limit Break, you'll find Aps much easier to defeat. This Limit Break will often paralyze Aps for most of the fight.
With Aps defeated, the party is ready to make the long trek trough the sewers to the Sector 7 Slums. With any luck, they can get there in time to prevent Shinra for destroying the support column.
Note:
There are few items to pick up in the sewers. The best of which is the "Steal" Materia. Equip it immediately, most likely using Tifa. Start filling your inventory with losts of stolen goods.
The team may be weak after fighting Aps. you should heal everyone before exploring the sewers.
When you exit the sewers, you'll appear deep inside the Train Graveyard. There are some particularly nasty beasts roaming around here, so save before you attempt to venture through the rusted wreckage.
You basically have two ways to get around the train cars: You can either go through the cars or crawl over them. Look for girders and gratings, because they serve as steps into or onto the cars. If you can't get down from a train car, look for an entrance. If you can't go through, look for a way out.
Note:
Beware of a creature named Eligor. You can steal a Striking Staff from it, which is Aeris' strongest weapon at this point in the game.
There are lots of items awaiting those willing to search them out, but not all of them are obvious. Make sure you collect the items concealed in the oil barrels that are spread around the train Graveyard.
A large pile of dirt blocks the exit. Cloud can't go over it or through it. So you'll need to create your own path to reach the exit. Hopping into the first train engine causes it to push one of the boxcars to the side. Now hop into the second engine and Cloud will move it between two more boxcars. in effect, this creates a bridge to the Sector 7 Station.