Great Sea Trench

- The next dungeon in your path is deep underwater, off the east coast of the eastern continent. It appears on the map as a deep scar. The usual Gargoyle duo is waiting in the entry hall; you know by now how to handle these cretins.

- B2. The enemies in here are largely fire-themed, so water and ice attacks are wisest. Head east to find a split, then go south to find a Water Scroll. East of the split is the exit, leading to a save point.

- B4. The switch on your left creates a path to the south. Head east and you’ll find another switch, though hitting it will only eliminate a shortcut north. There’s another room in the north; inside you’ll find a slew of switches, each of which will drop you down to B5. Use the closest switch, ‘cause the others will drop you onto patches of lava. (The only exception is the northeast switch, which creates a bridge in the northwest to a Flame Ring.) There’s a Dragon Fang in the north of B5 and an exit to the east.

- B6. Head southeast and you’ll find a lava patch; use Float to avoid damage and reach a chest containing an Ether. You’ll want Float active for most of this floor, speaking of which. There’s a Phoenix Down in the next chest to the east. The exit’s in the far east.

- B7. There’s a save point here, as well as a ‘Dwarven Kingdom’ of sorts. There’s a weapon and armour store in the northeast door; change the wares by approaching the dwarf from different sides of the desk. Down a southeastern passage you’ll find a dwarf who claims something odd is happening in a forest above him, and you’ll get a shot of the world map for reference. The exit is through the southeastern door.

- B8. (But not labelled as such.) This area has three sealed doors and a series of switches to the south. (Float is pretty much mandatory here.) There are many switches in this room, but the only one of use is the northeast switch; it opens a door a short walk to the west, opening up to a chest containing Kaiser Knuckles. Go up the stairs in the north and open the chest beside the sealed door to unseal the door. The tablet is straight ahead in the next room, as well as a boss battle.

Triton, Nereid, Phobos

Hey, remember those stupid Gargoyles you’ve been fighting all this time? That strategy applies here too. Triton, Nereid, and Phobos all have linked lives, and you need to kill all three within a reasonable time frame of one another in order to succeed. Fail to do so and they’ll come back to life within a round. They’ll also use their Delta Attack to mess up one of your characters pretty badly upon revival.

Each of them are of a different element (fire, ice, and poison, respectively), and will absorb those elements, so alternate elements (wind and water) or non-elemental, all-hitting attacks are advisable. Summons are quite effective here, particularly Odin, Bahamut, or Leviathan, the latter of which is found in the next dungeon. (Though you can do it first if you like.) It’s wise to throw up Reflect during this fight to block two of their three all-striking attacks, Blizzaga and Firaga, as well as Delta Attack in case one dies too quickly. With their spells blocked only Phobos is much of a threat, and even he is fairly weak.

Defeat the trio and you’ll be free to leave - though first you’ll learn Meteor, the best bit of Time Magic in the game.

Istory Falls

- In the second world there was a small cave on the shore of the northwestern continent which led to a Chocobo Forest and little else. In this world it’s in pretty much the same place, only now it leads to Istory Falls. Yes, the waterfall itself is a location.

- First up: this area is, generally speaking, filled with enemies who are weak to lightning. Those vulnerable to the element typically travel in packs, as well, so Lightning Scrolls and Thundaga make good choices.

- Hey, look, Gargoyles! How surprising. 

- To the north is a large room filled with waterfalls. Stepping into these waterfalls may sweep you off of ledges, so watch where you’re going. Make your way west - there’s a Turtle Shell and an Ether in chests to the right of your destination - and go north up the stairs that run through the middle of the room. You’ll find an Air Knife in a chest to the east of the exit.

- There are two doorways in the next room, though both lead to the same area. Take the right and you’ll find a Goliath Tonic to the south. Further south of here and on your right, in the corner of the room, is a secret passage that leads to a Rune Blade. There’s a switch in the wall to the west, north of the exit; hit it, then dash to the chest to your right before the water you stopped starts again. The chest contains a Protect Ring. Be warned! This area potentially contains a Tonberry, an extremely powerful enemy that will Knife your party to death after several turns of approach. Don’t fight unless you have a slew of hard-hitting spells or attacks on hand, and be prepared to run if things don’t go your way.

- B3. Head west to find a split in the winding path. There’s a Phoenix Down to the north and another split to the south; go left to find a chest containing a Reflect Ring. To the right and south is a save point.

- B4. Head south. There’s a doorway on your left leading to an Artemis Bow and stairs just south of the door down to B5. Ignore the latter for the moment and explore the southwest for 12,000 gil, then to the northwest for an Enhancer. Be careful walking to the northwest, as there’s a hole in the ground just south of the doorway.

- B5. There are chests in the open to the north, though if you approach them from the wrong angle they’ll sprout spikes and do massive amounts of damage. Approach the chest on the right from the bottom to safely get a Fuma Shuriken, and do the same for the chest on the left for an Aegis Shield. You can hit the switches near these chests to activate and deactivate the traps for safer passage. A final chest in the south, protected by spikes, contains a Titan’s Axe; there are holes around the chest if you hit the switch.

- B6. Tablet! Check it out, then head north to leave. You’ll run into a battle… though not with the beast you expect. Note that you can skip this fight if you wish, though you’ll have to make the trip through the dungeon to get to it again. The exit is the waterfall to the south, regardless of your choice.

Leviathan

You’re probably prepared for this fight already. Leviathan is a water-based foe, and it utilizes two all-hitting attacks - Aqua Breath and Tidal Wave - to dish out medium-to-large amounts of damage each round, the latter of which is the worse. It can also paralyze a single character, which it does somewhat often, and uses normal attacks. That’s honestly about it. Raise your defences, Slow Leviathan, and pummel the aquatic beast with lightning-elemental attacks. Thundaga can absolutely trash Leviathan, whether as a spell or as a Mystic Knight attack. Overall, not that bad a fight. You’ll get a Reflect Ring for beating Leviathan, and you’ll earn Leviathan as a summon.

Sealed Castle

By this point, assuming you’ve visited all of the optional dungeons and collected the four tablets, you’ll be able to grab all twelve of the special weapons from the Sealed Castle, which is now a short trip northwest of the Pirate’s Hideout. Enter the room with the weapons and lay the tablets on the stone table by the entrance. This will allow you to unlock three of the weapons. Lay down all four to get all twelve weapons, which include Excalibur, Assassin’s Dagger, Sasuke’s Katana, Holy Lance, Rune Axe, Masamune, Yoichi’s Bow, Fire Lash, Sage’s Staff, Magus Rod, Apollo’s Harp, and Gaia Bell. There’s pretty much one weapon for every class to use.

Once all of the weapons are unlocked and collected you’ll get a message about an earthquake on the way out of the Sealed Castle. Head south on the world map and, just south of the thin line of land that stretches across the southeast corner of the ocean, you’ll see bubbles on the surface of the water. Submerge your ship and you’ll find a scar in the seafloor. Debark here and you’ll find a room with a few sealed doors… as well as the Oracle, Gladiator, and Cannoneer crystal shards. There’s an entire dungeon to be found here, as well, though you need to complete the game first.