Based in Port Douglas Australia, Poseidon operates a 5 star cruise to the Great Barrier Reef. Snorkellers & Scuba Divers can enjoy 3 spectacular sites at the Agincourt Ribbon Reefs of the Great Barrier Reef. Poseidon III, the ultra modern high speed catamaran gives "The Ultimate SNORKEL & SCUBA DIVE Adventure" on the Great Barrier Reef from Port Douglas Australia. We take you to the very edge of the outer barrier reef - Agincourt Ribbon Reefs. With access to more than 45 locations at 16 different reefs - 3 sites are chosen each day according to tidal & weather conditions. Swim - Snorkel - Dive or Simply Relax