Goat Island is the island where Luffy first met Coby and Alvida. This island appeared only in the manga, while in the original anime, Luffy met Coby on the Lady Mary. The island was later included in the special Episode of Luffy.
It is a small, rocky island where small rocks covered the shoreline and a small forest is visible.
At some point, the Alvida Pirates made this island their base. After making Coby their chore boy, he planned for years to escape, building a small boat near the forest.