Eden and Atlantis.
More exactly, this sunken continent was Lemurian Atlantis, the larger of the two Atlantises mentioned by Plato. Lemuria was the vast prairie which the Greeks called Elysian Fields and which the Egyptians named "the Field of Reeds" (Sekhet Aaru) or, yet, "the Ancestral Land" (To-wer), the overseas Paradise where they formerly lived, in Zep Tepi ("Primordial Time"). The sunken continent became the Land of the Dead, the dreadful, forbidden region where no mariner ever ventured to go, for it was "the Land of No Return".
Interestingly enough the name "Ancestral Land" (or Serendip) is precisely the Dravidian name of Taprobane (Sumatra), the island where the Hindus placed their pristine Paradise, likewise sunken in a cataclysm. The gloomy, pestilential place that remained above the water was named Sheol ("Hell") by the Jews, and, in the spared spots, "Island of the Blest" (Makarion nesos) or Hades by the Greeks, Amenti or Punt by the Egyptians, Dilmun by the Mesopotamians, Hawaiki by the Polynesians, Svarga by the Hindus, and so on.
The Celts — whose legends are perhaps the best recollection of the sunken golden realm — called the place Avallon, Emain Abbalach or, yet, Ynis Wydr ("Island of Glass"). They also associated the eerie place with the Holy Grail and the resurrection of their dead heroes, as we detail in other, forthcoming articles of ours. And we already mentioned above the Yvymaraney of the Tupian Indians of Brazil, or the Aztlan or Atitlan of the Mayas of Yucatan, the submerged land which these Indians were obliged to flee, when it sunk underseas.