Take the path up into the trees and search for a Sleepy Cait Sith on the right side.
Further along you'll come to a chest with 2000 gil.
In the next section, just before the downward loop, there's a chest on the right with 3 Phoenix Downs.
After the bird guy, go on to the next section and look for a hidden chest with a Remedy on the left.
In the next part, pick up the Al Bhed Primer XV near O'aka.
Just past O'aka, Auron will open up a new path for the party.
Follow the path in to where you'll battle Spherimorph.
Afterward, you'll find your first Jecht's Sphere.
Go back to the main path and head north to reach Lake Macalania.