Aldabra is one of the world's largest coral atolls, stretching 22km (14mi) east to west and enclosing a huge tidal lagoon, which is sometimes home to tiger sharks and manta rays. Aldabra is the original habitat of the giant land tortoise, and there are about 200,000 of them on the atoll, as well as thousands of seabirds, including the white-throated rail, the sole remaining species of flightless bird in the Indian Ocean.Assomption Island, 27km (17mi) south of Aldabra, was once a rich source of guano, but the harvesters who exploited the island also stripped it of vegetation, so that by the 1920s no plants, animals or birds lived here. Underwater, however, it's a different story: Jacques Cousteau filmed most of his documentary, The Silent World, here, and said he'd never seen any other place on earth with same clarity of water or diversity of reef life.The only people who live on Aldabra are scientists, and they're only here three months of the year. Aldabra is more than 1000km (620mi) from Mahé, and there are no hotels here. If you want to visit Aldabra, you'll have to organise a boat with the Marine Charter Association in Victoria, or fly to Desroches and charter a boat from there.

This island, just 1.5km (1mi) off the north coast of Praslin, was a leper colony from 1833 until 1965. The ruins of the leprosarium still stand on the south coast, like an early holiday village. You can still see the old doctor's house, a Créole home with a spacious verandah, which has been declared a national monument. The only people who live here are the island manager and several park wardens, but if you're feeling lonely have a chat with the couple of hundred giant tortoises that roam the island. The island is an official marine national park, and you'll have to take a guided tour if you want to wander around. Apart from the tortoises, it's worth looking out for the island's stunning granite sculptures. The best way to get to the island is on an organised tour.

About 20km (12mi) from Mahé, Silhouette is a large granite island which rises steeply from its beaches to three high peaks. Visitors have described this island as eerie and mystical - it looks particularly dark and mysterious at sunset. Rumour has it there's pirate treasure in the hills - whether it's true or not, there are some interesting caves. The beaches on Silhouette are protected by a reef and are great for swimming, snorkelling, or lazing around developing melanomas.If you're after something a bit more strenuous, take a walk to the top of Mont Pot à Eau to see the bizarre carnivorous pitcher plant. Along the track you'll see coco de mer palms and monstrous millipedes, slugs and snails.You can get to Silhouette by helicopter from Mahé, or you can join a tour, arrange a package deal or charter a boat.