Rusukaina

Rusukaina is an island in the Calm Belt that is to the northwest of Amazon Lily. It is a harsh island that has forty eight seasons with the season changing weekly. There are several different species of dangerous animals on it. A country supposedly used to exist on this island, but its people could not survive against the extreme environment and died out. According to Silvers Rayleigh, when Luffy arrived on the island, there were over 500 beasts living there he would not be able to defeat. Rayleigh took Luffy here to train him in the use of Haki for 2 years. After 2 years, Luffy became the "boss" of the island, even befriending some of the animals (which Luffy considered a mistake, as he couldn't eat them).

Trivia

 * "Rusukaina" means "Anybody home?"