These were the islands in Mother 3 where the Dark Dragon had been sealed away by the Magypsies using the power of the Seven Needles. Because of the dragon slumbering beneath the islands, the islands were protected from the apocalypse. The last remaining humans reached the island and erased all memories of their previous lives so that humanity could have a fresh start. The islands are made up of a main island, Tanetane Island and perhaps another unknown island where New Pork City is located.
In Mother 3.5, the islands have a different backstory. There are also several more islands.