Rusukaina

Rusukaina is an island in the Calm Belt that is to the northwest of Amazon Lily. It is a forty eight season island whose climate changes every week. There are several different species of dangerous animals on it. According to Silvers Rayleigh, when Luffy arrived in the island, he would not have been able to defeat more than 500 beasts living there. Rayleigh took Luffy here to train him in the use of Haki for 2 years.

Trivia
"Rusukaina" means "Anybody home?"