Christmas Island is Australia's remote Indian Ocean outpost, where a narrow fringing reef drops into deep blue water almost immediately. Expect wall dives, caverns, and drift dives off Flying Fish Cove, plus a real chance of whale sharks and mantas in the warmer, wetter months. Snorkelers can keep it simple at Flying Fish Cove or switch to Ethel, West White, and Dolly Beach when conditions change. Freedivers love the island's signature feature: the bottom can fall away to hundreds of metres within a short swim from shore. Topside, Christmas Island National Park is famous for the red crab migration and endemic seabirds you will not see anywhere else. The trade-off is remoteness: limited flights, limited services, and no recompression chamber, so book early and dive conservatively with the right insurance.