In Atlantis, the player controls the last defences of the City of Atlantis against the Gorgon invaders. The city has seven bases which need to be defended. Three bases are equipped with cannons to destroy the invaders who are dropping bombs from above. The gun bases have fixed cannons. The center base fires upwards, while the far left and far right bases fire diagonally across the screen.
The enemies fly back and forth four times before they begin bombing. Destroyed bases can be repaired if enough Gorgon ships are destroyed.
Gameplay continues until all the bases are destroyed.
The game is followed up by its sequel, Cosmic Ark.