The largest, and central, of the 5 islands and the only natural island in the small island chain is what led to this island getting the prime designation. The island is just a bit over 100 sq. mi. in size and is home to most of Atlantis’ residents, and the town.
Being the only natural island means it is the one with the unplanned geography, though they have done their best to take advantage of the natural geography. The mountain that takes up about a quarter of the island has been given the name Little Olympus, and they have put a private resort for the locals on the mountain that is called The Palace.