Zanzibar can be reached by plain or by boat from Dar es Salaam.
Although taxis are available, you will probably want to walk through Stone Town. Journeying outside Stone Town is most comfortably done with a taxi or a private car, however a network of dalla-dallas, small minivans, exist which service all the major villages on the island.
Things to Do
Zanzibar Island, a.k.a., The Spice Island, was an important stop in the Spice Trade centuries ago. Today, it is one of the few places in the world where saffron is produced, and many other Middle Eastern/Asian spices (cardamon, ginger, cloves, nutmeg, etc.) are grown here. For $10-$15 you can go on a spice tour, which winds you around the island, showing you how anise (licorice) grows; letting you sample some of the exotic fruit grown on the island; and allowing you to tour the beautiful plantations.
Jozani Forest has excellent nature trails, featuring some very exotic (and large) trees. Even more interesting, though, are the Red Colobus Monkeys that live here. Native to the Island, these monkeys are now nearly extinct. They are very curious and playful and will likely pose for a picture. The entry fee also includes an optional visit to a beautiful mangrove forest which is highly recommended.
Stone Town, recently declared a UNESCO World Heritage Site, is one of the most unique cities in the world. Blending Moorish, Middle Eastern, Indian, and African traditions and architectures, it is possible to spend days winding through Stone Town's labyrinthine alleys; shopping; drinking tea; and visiting the city's historic sites. Visit Slave Market, The site of the old Slave Market is quite an experience. Go into the holding chambers to see how this wretched piece of history played itself out in small dark dungeon-type cells.
Visit Forodhani Gardens If you are not scared of local food, then this place is definitely worth a visit. It is possibly the cheapest food you will find on the island, and value for money too. Ranging from crab claws, calamari steaks to plain old chips done in big woks. You are well advised to try the local sugar cane juice. The curio market can be found next to the food market. Here you will find all the gifts you may want to take back to friends and loved ones.