Final Fantasy 1 Mt. Duergar and Melmond

Items: 575 Gil, Cottage, Tent
Equipments: Wyrmkiller, Mythril Knife, Helmet, Mythril Mail, Grand Helm

It's time to take your ship, and sail towards the port located northwest of Cornelia. Dock the ship there, and continue heading southwest, until you spot a cave that's surrounded by mountains. Proceed into the cave.

There is a mystic door at the bottom-left section of this area, with these treasures inside -- "WYRMKILLER", "MYTHRIL KNIFE", "HELMET", "MYTHRIL MAIL", "575 GIL", "COTTAGE", "TENT", & "GRAND HELM".

Once you've collected everything, exit the room and talk to the dwarf standing at the right side. Hand over the Nitro Powder. A new passage is now accessible, so make return to where you docked the ship. Sail west through the canal, dock once again at the nearby port & head into Melmond.

This town has plenty of expensive but useful magic spells. Pick up Cure 3, Dia 3, Life 1 & Heal 2 for white magics. For black magics, you might want to get Fire 3. The weapons here aren't all that powerful, so you should be fine with what you already have. (Assuming you picked up all the Mystic treasures earlier.) Exit back to the world map when you're ready. Also, be sure that you have some Antidotes & Gold Needles in stock. Otherwise, go back to a town with an an item shop, and buy some before proceeding.

From Melmond, head west until you see a long stretch of coastline going south. Go that way, and around the mountains further ahead to the Terra Cavern.