Captain Rhama Sabrier is invited by the old healer Areliano to investigate the appearance of a mysterious ship below the island. Rhama finds out that the ship was used to transport rare healing herbs and contains the clues for finding them and bringing them to the healer. But at this point everything goes wrong. Rhama and Areliano are betrayed, and soon the Captain finds himself on the run; but that doesn't mean that he abandons the quest. Aided by Faith, Areliano's lovely daughter, and other friends he meets on his journey, Rhama is determined to bring the betrayer to justice and deliver the ship's legacy to the right hands.

Galleon is a 3D action game with platforming elements, created by the designers of the original Tomb Raider. Like in most other games of this kind, most of the gameplay is dedicated to jumping and climbing, with some combat thrown in. However, Galleon includes many less typical elements. Rhama possesses extraordinary acrobatic skills and can run on walls and perform very long jumps. The game has an unusual control scheme, which makes Rhama respond to the amount of pressure the player applies to the analog stick, allowing various and precise combinations of running and jumping, including the possibility to influence character movement during free fall.

Further stand-out features include cooperation between characters (similarly to ICO, though Rhama has two female companions), treasure hunt system (Rhama can use his pirate senses to discover hidden treasures), and boss battles that require climbing on the enemies to destroy them, Shadow of the Colossus-style.