Goblin Island is a large island located in the northeast portion of the map. It can be seen very clearly from the world map.
There is only one primary reason to visit Goblin Island and that is to seek out the Goblins who inhabit the island. Firstly, this is to obtain the rare 
Zeio Nut item which is used for breeding Chocobos. Secondly, you can also obtain the enemy skill Goblin Punch for your 
Enemy Skill Materia.
Use the link below for more information on how to race and breed Chocobos:
The Goblins only appear in the forested areas of the island.
The map below shows the location of the Goblin Island on the World Map:
