Nanimonai Island

Nanimonai Island (the Island of Nothingness in the English manga translation) is an uninhabited island just beyond Alabasta.

Miss All-Sunday gave Luffy an Eternal Pose to this island to help the Straw Hat Pirates reach Alabasta, but Luffy destroyed the pose, refusing to let her, an enemy, choose their route.

As confirmed during the Little Garden Arc, this island is actually feces left by a giant goldfish, one of Usopp's lies becoming true.

Trivia

 * "Nanimonai" means "nothing" in Japanese.