Mt. Nibel

Follow the winding path left and up. There's a side path that leads up to a chest with a Rune Blade in it. Continue on and just before the bridge, there's another side path that leads up to a Plus Barrette.

Cross the bridge and enter the cave. Inside is a series of tubes which you can slide down. Before going down any of them, climb down the stairs and ladders to the bottom floor to push down the folding ladder so you can get back up.
Chute #1 leads to the bottom floor.
Chute #2 leads to a rock where you can pick up the Powersoul.
Chute #3 leads to the middle level.
Chute #4 leads to a chest with an All in it.
Chute #5 leads to the middle level as well.
Once you've collected everything in the room, take the exit to the left of the big scorpion monster on the bottom level.

Drop down off the ledge and enter the small cave just below the exit. Follow the path up to the right and then go in the hole on the left, following the hidden passage down to reach the chest with the Elixir. Head out through the top exit.

Grab the Elemental by the fountain and then continue on. Inside this next cave, head up and left to find a Sniper CR in a chest. Exit to the right and down.

Take the left path and follow it around until you come to the Nibel Reactor. There's nothing to do inside this time so just go past it and enter the door behind it to return to the room with the chutes.

This time, confront the giant scorpion monster which happens to be the Materia Keeper. Grab the Counter Attack that it leaves behind and then leave through the exit it was blocking. This path takes you to the other side of the mountains.

Obtain: Enemies:
Notes: Try and steal some Gold Armlets from the Dragons.