Dive into the water. Progress deeper and deeper avoiding dangers and collecting valuable items. But never forget to pay attention to your limit of oxygen. Go back to your underwater capsule to refill your lungs with fresh air and to stock your items, not to loose them.
The game ends when a player spent all her oxygen, or when all 36 transparent cards have been discarded. Then the player having the more victory points (through the collected items) win the game.