For the first section, Yuna starts out alone.
Head east and then north to find Kimahri and a chest with a Mega-Potion.
Head north from there until you run into Auron.
Go west until you reach a locked room with some chests inside.
Head south from there until you come to a pad.
Go east to find Lulu and a chest with a Wht Magic Sphere.
Continue south until you find a chest with an Elixir and a strange symbol on the wall.
Touch the symbol to activate it then head north and east to return to the beginning.
Go north past the first chamber and hang a right.
On the the north side is a chest with a Blk Magic Sphere and a glowing tile.
Step on the tile and then go back and north to where you met Auron and go west until you see the teleport tile.
Step on the tile when it is pointing west to be teleported into the locked room.
The 3 chests inside contain a Skill Sphere, a Lucid Ring and 10000 gil.
Return to the place where you found Auron again and take the reddish north path.
Issaru will attack with his aeons (Pterya, Grothia
and Spathi) and Yuna will have to defend with hers.
Tidus, Wakka and Rikku must now find their way out.
Follow the underwater tunnel until you come to a large circular chamber.
When you enter, you'll have to fight Evrae Altana.
If you defeat it without using the trigger commands, you'll be able to pick up the Rematch and Avenger
in the tunnels on the way to the exit, otherwise, they'll be locked behind the door.
Just as the party is reunited, you'll be confronted by Seymour.
Kimahri stays behind to stall him while the rest of you make your escape, but
Yuna changes her mind and goes back for him, with the rest tagging along.
At the other end of the bridge, you'll rejoin Kimahri and take on Seymour Natus and Mortibody.