Fish-Man Island

The Underwater Wonderworld Gyojin Island
The island that appears to be underwater. "You'll understand how to go down when you'll get there," as was stated by Kokoro, claims that there is a unique way of getting down there.

The Florian Triangle
The island is protected by a horrifying place that sucks ships and crews to an unknown fate. It is stated that 100 ships disappear there every year.