Aldabra Atoll, situated 1,150 kilometres south-west of Mahé, is the largest raised coral atoll in the world, comprising more than a dozen islands bordering a lagoon so vast the whole of Mahé could fit inside its perimeter. Aldabra’s exceptional and pristine condition has earned it the distinction of being named a UNESCO World Heritage Site, one of two such sites in Seychelles. The atoll’s islands nurture a vast array of both unique flora and fauna as well as the world’s largest population of 150,000 giant tortoises, and its lagoon boasts the most vibrant marine life of the entire archipelago. First given its name by Arab seafarers, the atoll’s harsh, sun-baked environment and the fast-flowing waters of its lagoon typically kept all but the most intrepid explorers at bay. But there has been a tiny permanent settlement on the island since 1874, made up chiefly of contract labourers from Mahé engaged at different times in fishing, mining guano and producing coprah for sale on the mainland. The Seychelles Island Foundation (SIF) now supervises the island and strict regulations governing the island’s accessibility are in force to protect its fragile ecosystem. A small research station affords accredited scientists the opportunity to study the atoll's biodiversity, but there is no hotel accommodation on the island. Yacht charters are available, however.

Assumption Island

The island of Assumption lies 1,140 kilometres south-west of Mahé, some 40 kilometres west south-west of Aldabra, and is nearly 7 kilometres long and 2.5 kilometres wide. There is little activity on the island although an airstrip was built in 1990 with aircraft from Mahé serving the island on a charter basis, chiefly for scientists visiting neighbouring Aldabra. Assumption is a nesting site for turtles and its surrounding waters, accessible mainly by chartered yacht, are excellent for diving.

Astove Island

Astove Island is located 1,045 kilometres south-west of Mahé and 160 kilometres west south-west of Aldabra. It is one of the most southerly links in Seychelles’ chain of islands. The atoll is encircled by a coral reef and features a shallow lagoon. Astove is a turtle nesting site and offers the experienced diver extraordinary diving opportunities along the sheer walls of its spectacular coral rampart. Astove also has an airstrip and is serviced by aircraft from Mahé on a charter basis.

Cosmoledo Atoll

Some 1,045 kilometres south-west of Mahé and 120 kilometres from Aldabra, the atoll of Cosmoledo comprises a ring of nine main islets surrounding an inner lagoon roughly 16 kilometres long and 11 kilometres wide at the widest point. The sea around Cosmoledo is particularly rich in fish while the atoll itself is home to large colonies of frigate birds, terns and boobies. This hauntingly beautiful atoll is also a nesting site for green turtles.