One player takes on the role of Poseidon, while the others – from one to four players – become the Navigators in search of the Sacred Island.
The game is played over two copies of the same board, separated using the box so that they are not visible to each other.
As Poseidon, you throw powerful storms against the Navigators, driving them off-course and confounding them, so they cannot reach the Sacred Island in time. Only Poseidon knows the real position of the ships, indicated on his copy of the game board.
The Navigator players sail through endless storms, blind to all around them, trying to gather clues to their whereabouts to stay on course. They also keep track of the position of the ships on the board, but the positions indicated there are only their best guess, and they can become very inaccurate as the game goes forward!
The Navigators must reach the Sacred Island before the end of the game to win, using their wits to stay on course, while Poseidon wins by preventing the other players to reach their destination.