The island of Unguja (commonly known as Zanzibar) has the best beaches followed by the south coast of Dar es Salaam and Mtwara. Long stretches of palm trees, unfortunately in many cases packed with hotels and guest houses, although it is still possible to feel in some areas that you are alone in the world. The Stone Town is well worth a visit of at least one night.

The islands of Mafia and Pemba have incredibly rich waters but the coasts are mostly covered by mangroves. Still you can  reach untouched sand bank where you will for sure be alone in the world. Their infrastructure is minimal and the crowds non existent. They are ideal for honeymooners.

Diving: Tanzania offers excellent diving and snorkeling opportunities from the islands of Mafia and Pemba and from the southern town of Mtwara.  The diving in Zanzibar is only recommended for travelers who just want to do a couple of dives as a complement of their holidays.