The explorer David Livingstone, docking in Stone Town's port in 1866 when it was the most important trading centre on the coast, condemned the main town as "gross and crass" and coined the nickname Stinkibar. Yet explorers and visitors in equal measure have been entranced by the scent of sandalwood and udi (incense smoke), by the decaying houses with their beautifully carved doors left slightly ajar, that seem both to invite and forbid foreigners from exploring the shadowy courtyards within.
The secret to exploring the "Venice of Africa" - so-called because seasonal downpours turn the town into a labyrinth of silted streams - is to ditch both watch and guidebook and get gleefully lost on purpose in the often unnamed streets. In fine weather the experience is akin to rambling through a series of alfresco living-rooms. Beautiful women float past in green, pink and orange veils revealing a glimpse of hennaed hands or feet. Teenagers cycle after you, keen to practise their English. Greetings echo along the lanes as you dip into fusty curio shops that sell anything from silver jewellery to fragments of stone fretwork, and bazaars you may never find again. Without warning you turn another corner and emerge blinking in the sunlight, face to face with the Indian Ocean. In the Jamituri Gardens near the port, where Zanzibaris congregate in the evenings to eat and socialise, the smell of putrefying rubbish mingles with aromas from street vendors cooking clove fish cakes, miniature spicy kebabs and shreds of pickled octopus, and serving passion fruit juice flavoured with tamarind or sugar-cane juice mixed with lemon and ginger. Young men push the end of a long sugar-cane stick into a mangle while others rotate the handle, the thirst-quenching liquid pouring into an ice-laden bucket into which you dig your glass. Small boys hurl themselves into the dhow-dotted ocean as the setting sun bathes everyone in its warm glow.
This is a place that demands and inspires respect. Zanzibaris are proud and independent, and view their island as a separate state within Tanzania. A resident told me that tourism had only truly taken off after the first multi-party elections in 1995, and that foreigners offend the mainly Muslim population by wearing swimming costumes in town or by "making loving on the beach". At the airport leaflets are handed out telling you not to buy corals or products made from endangered sea turtles and not to photograph anyone without their permission. Brutalist western hotels are beginning to spring up in the new part of the town, but are less intrusive than the reconstruction projects. You get the impression that by the time the last building has been salvaged, the first will be threatening to collapse again.
Arab, Persian, Indian, African, Portuguese and even British cultures are as intertwined here as the carvings on the house doors: the more elaborate an owner's portal, the greater was his social standing. Zanzibar's trading history dates back to the second century BC when Chinese silk and porcelain reached the island via the Silk Route from China to India. The tale of Sinbad the Sailor was probably inspired by accounts of Arab sailors voyaging to East Africa and Asia. During the eighth and ninth centuries, immigrant Arab and Persian sailors traded African gold, ivory, rhino horn, leopard skins, tortoise shell and ambergris with their original homelands. After Portuguese occupation in the 16th and 17th centuries, during the rule of the Omani and Zanzibari sultans, thousands of African slaves were transported via Zanzibar to plantations in Oman and the East Indies. While the name Zanzibar comes from the Persian meaning "land of the black people", the Swahili name - Unguja - translates as "bowl of fruits". Zanzibar and her sister island Pemba are the most fertile of any lying off the East African coast. During the latter half of the 19th century the islands produced over 90 per cent of the world's supply of cloves, the dried, unopened buds of the clove tree. The most widely accepted story is that clove seedlings were brought from Mauritius by a Zanzibari Arab who had been banished for murder by the sultan, but whose good deed earned his pardon. With abundant slave labour the royal plantations prospered until a freak hurricane destroyed virtually all the clove trees in 1872. Since the majority of present-day trees date from the replanting in 1873 - the same year as the closure of the slave market - output is now lower and of an inferior quality.
A spice tour is an educational and gluttonous experience. For just a few dollars you can spend a hot but fructuous morning rattling in a truck- cum-minibus visiting plantations, gardens and Persian baths with a herbal guru. Mitu, sun-wrinkled and charismatic, is the most renowned of herbal guides and has been leading tours for 37 years. His approach to teaching is sensory: he picks fruit, seed pods and leaves and invites you to smell, taste and pull apart the samples while he provides a fascinating running commentary about growth patterns, harvesting and medicinal uses. He even swears he can cure hepatitis or yellow fever in a couple of weeks using sugar-cane juice and coconuts.
Mitu tells us that drinking an infusion of 40 crushed cloves boiled in water cures diarrhoea. The oil is good for massage and toothache, he adds. Next we inspect a pineapple tree, a perennial herb. The juice aids digestion, is a cure for stomach ache and is used to promote the healing of wounds. Mitu points out a banana "tree". Although the plants grow up to 20ft tall, the trunks are false since bananas are in fact herbs. We are standing beneath a sandpaper tree: everyone is given a leaf, and Mitu instructs us to trundle off to the nearest building to attack the wooden door. It works a treat. Just like commercial sandpaper, one side is rough and the other smoother. Cayenne pepper, we learn, comes from the elongated, bright red chillies that hang from a leafy plant. Apparently it is used in the making of tear gas. Thoroughly impressionable, we can't tell whether Mitu is teasing us with the Zanzibari equivalent of spaghetti tree jokes.
The latter part of the tour is spent wandering in single file through Mitu's specially created tutorial garden. New sensory experiences rain down thick and fast. Jackfruit, huge and oddly shaped, hang from trees like swarms of bees. They are highly aromatic and taste like a cross between pineapple and banana. Mitu describes mangosteen as "the best fruit in the world". Each fruit has marks on its underside showing how many seeds are inside. Five seeds makes for the tastiest, snow-white flesh. We learn about rambutans, sapodilla plums and papaya, but we do not catch sight of the infamous durian. The tour ends with a feast of spiced rice and spiced vegetable stew followed by watermelon, starfruit, spiced sweets and spiced tea.
Sated with delicious spices, all visitors seem to head for Zanzibar's paradisiacal east coast at Paje or to Nungwi on the north coast. Paje is a fishing village where at low tide women and children collect shellfish and seaweed from the shallows. Seaweed, exported as a thickening agent for food, is a growth industry. At high tide fishermen cross the reef in dugouts made of baobab wood with outriggers. Every morning after sunrise the clouds disperse and the day settles into its perfection. The pale turquoise sea darkens into a purplish blue over the coral reefs. The sand underfoot is soft and creamy as silk. Majestic palms sway in the winds, their fronds long and elegant as green gloved fingers. Days drift by watching life move at a pace as slow as the ancient, giant tortoises on Prison Island, a stone's throw from Stone Town, where recalcitrant slaves were once detained.
Aim to go during the dry seasons from December to February or June to October. In the wet seasons the hotels are empty, and the downpours are still interspersed with brilliant sunshine. At Christmas and Easter the island is a popular short-break destination for expats from Dar es Salaam and Nairobi.
There are no direct flights to Zanzibar from Europe. Your best option is to fly to Nairobi and go by Kenya Airways (pounds 167 return) or Air Tanzania to the island. Gulf Air (changing planes in Abu Dhabi or Muscat) and Oman Air (changing in Muscat) fly from Europe. Prices start from pounds 401 during the low season (March to mid-July) and pounds 531 in the high season (mid-July to mid-September and December). If you want the scenic route, you could take the wonderful Nairobi-Mombasa train and fly from Mombasa (pounds 76 return with Kenya Airways). Another option is to take a ferry from Dar es Salaam ($25 one way), although this choice was regretted by most people I met. A useful starting point is the Africa Travel Centre: 0171 387 1211.
A three-month visa costs pounds 38.
Foreigners need US dollars for big bills - flights, accommodation, tours - but everything else is in Tanzanian shillings. If you're on a shoestring, you can get away with paying in shillings for hostels. There are very few hotels that accept credit cards, and don't expect to get cash advances on your Visa - it's virtually impossible.