Deep Sky is a location accessible through the Vortex beneath Shrine Island.
Known only through legends and myths as the Land of the Dead, Deep Sky is a collective reference to the actual, physical surface of the planet Arcadia, where the atmospheric pressure is too high for most lifeforms to exist, let alone thrive. Sunlight also cannot penetrate into Deep Sky, making the region incredibly dark and difficult to explore. Any ships that are sunk in the skies above wind up in Deep Sky, never to be seen again.
Deep Sky is the current home of the entire continent of Soltis, and where Zelos lived for centuries before being awoken.
Exploration into Deep Sky is possible given the latest advances in Valuan technology. Dangral Island was built solely to penetrate into Deep Sky and access Zelos's resting place on Soltis. Both the Chameleon and the Delphinus are outfitted to explore Deep Sky, but after De Loco's death, the Delphinus remains the only ship in all of Arcadia capable of exploring Deep Sky.