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. On this island there is only one safe spot, near a tree that resembles a Daft Green from Merveille.

Trivia

 * "Rusukaina" means "Anybody home?"
 * It was stated that the Grand Line has 16 Seasons. How this island has 48 is yet unknown...