Go north through the mountains until you enter the mountain path up to Mt.Nibel. You should remember this place from Cloud’s flashback. Follow the path until it splits. Take the north spiralling path to get a Rune Blade. Go back to the path and continue following it. Before the bridge, you can follow the other path to eventually get a Platinum Barretta. Go back to the bridge and cross it. You’ll come to a set of tunnels, go down the ladder and free the ladder that is folded. Go back up and go down the tunnel numbered ‘2’.
At the end is a Powersoul. Jump off the ledge and use the Save Point if you like. Climb back up to the top where the tunnels start and now go down the one numbered ‘4’. You’ll get an All materia in the chest here. You can now fight the boss, or go out the passageway next to the boss, and follow the path to go outside, then drop down to the lower ledge and enter the cave and take the right hand path. Work your way south west and go through the small hole. Go up, left then down to get to a chest with an Elixer in. Go out the exit to get to a wooded area. There is an Elemental materia on the ground to the left. Keep going north, then right, up as far as you can go, then left to get a Sniper CR. Go back and take the right most passage, this goes south and leads you outside. From here go left until you get to the Mako Plant in Cloud’s flashback. Go past it to the door set in the rock face. This will lead you back to the area with the tunnels. Head to the bottom and examine the blue bird-like creature to enter the boss battle…
This boss can use an attack called Trine, so you should learn it if you have Enemy Skill materia equipped. You should Haste to start off and make sure you have Cure/All equipped. The boss can heal himself too. Try to use physical attacks and save the MP’s to cure yourself. You can poison it as well. Just stick to Limit Breaks and physical attacks, you can use Summons as well to inflict more damage. You’ll get a Jem Ring when you win.
Pick up the Counter materia that’s left behind and go down the path that the boss was blocking. Follow it until you reach the World Map. Circle around the mountain until you see a town in the distance. Make your way towards it.