The Island of Atlantis was an island where all Atlanteans once lived in peace and harmony a long time ago. It was located in an unknown area in the middle of the Atlantic Ocean until it sank.
The Atlantean architecture was very much like those of the ancient civilizations of Greece and Rome, with tall pillars carved in marble and buildings with triangular roofs and domed ceilings. This may have indicated that Atlanteans either existed around that era or even before the classical civilizations. This may be why Fu Dog wanted to travel back in time in order to see the race's birthplace.