Mystery Island: Undiscovered, unspoilt paradise. THE BIGGEST mystery about Mystery Island is that nobody lives there. Barely a kilometre long and 200 metres wide, it sits off the bigger island of Tanna on the southern tip of Vanuatu. * This well-written article was issued in 2005 but the island information is still valid. Even though the Pacific Sun has since departed our ports, the P&O ships on-board activities are still similar, relevant and just as much fun.