Coral Princess: Cairns to Papua New Guinea
Credit: Louise Heusinkveld / Getty Images

It's the rare cruise that sails to one of the world's last frontiers. Australian cruise liner Coral Princess offers an extensive, 25-night exploration of remote Papua New Guinea by sea aboard the Oceanic Discoverer, which has just 36 staterooms. The luxurious ship departs from Cairns, the chief port along the Great Barrier Reef, and stops over in Indonesia's idyllic Raja Ampat, a spectacular area at the heart of the coral triangle, before loitering along PNG's wild coast and returning to Darwin in Australia's wild Northern Territory. Shore excursions are fraught and the snorkeling is remarkable. Shorter PNG-only itineraries take cruisers from Alotau to Rabaul to see the primitive artists of the Sepik river, the Tufi fjords – picture a tropical take dropped on Norway – and the traditional cultures of the Trobriands.