Cardia
As you explore the north with the AIRSHIP, you will likely notice a series of thin islands between the northern continents. These islands are littered with cave entrances. This is Cardia, home of the Dragons. You'll find various Dragons that provide information about the Test of Courage you are given by BAHAMUT, the Dragon King. There is also treasure to be discovered in three of the caves.
The Western Island
The entrance furthest to the west, on the island with the lighter grass, leads to a cavern with two treasure rooms. Your total haul here is 575 G, a CABIN, and a SOFT Potion.
The Southwest Island
The large swampy island, central among the southern trio, contains 510 G and a HOUSE spread across three treasure boxes. You will need to land the AIRSHIP at the eastern end of the island.
The Northeast Island
There is no treasure to be found on the smallest of the Cardia Islands.
The Southeast Island
The large forested island to the east holds the largest treasure haul, a series of treasure boxes offering a total of 18,335 G spread across two treasure rooms.
BAHAMUT's Island
The northwestern island is the only one with two entrances. You'll find no treasure in either, but the eastern entrance leads to BAHAMUT's throne room. He asks the party to prove its courage, and you would be wise to do just that.