Though the competition for No. 1 island in Australia, New Zealand, and the South Pacific is steep (consider Bora-Bora, Fiji, and Tasmania), the Great Barrier Reef, which unfurls from Australia’s northeastern coast, has taken the No. 1 spot seven times since 1998. The area’s spectacularly cerulean water and vast sweep of coral teems with sea life—baleen whales, leatherback turtles, giant clams, and 400-odd other species. Above the surface, it’s a menagerie of a different kind: a collection of hotels and island resorts, each with its own oceanfront appeal.