Mafia Island is a sleepy backwater that's rarely visited and in some ways is reminiscent of what Zanzibar looked like 30 years ago before the onset of mass tourism. There are some nice beaches, cashew nut and coconut plantations, and mangrove swamps, and deep-sea fishing, scuba diving and other watersports are available.
(Don't worry: The island's name is derived from the Arabic word for group—as in group of islands, rather than a group of gangsters.) Mafia will appeal to serious anglers or anyone in need of relaxation. Part of the island is protected by the Mafia Marine National Park, and the fish and coral life are quite spectacular. There are only a handful of lodges on the island, all at the top end of the scale, which can organize all activities. The views are amazing. Perhaps you should consider visiting Mafia soon; large deposits of gas and oil have been found offshore and if exploration begins, this will probably change the nature of the island considerably.
80 mi/130 km southeast of Dar es Salaam.