But the best thing about Chumbe is the bandas. A narrow, sandy path leads to your own, private, Tarzan-and-Jane fantasy house. Seashells line the driftwood steps into the living room and on a smooth turquoise floor, white tiles pick out the shape of a crab. Everything is propped up, lashed together, woven out of grass, or made of flotsam and jetsam. Hanging from the ceiling, a rope hammock full of brightly coloured cushions swings in the sea breeze. There is no garden fence, not even much in the way of walls, but the green, tangled jungle creepers that surround the place on all sides cut off all hint of other people - you might be utterly alone with the roar of the surf. Strange, exotic birds fly into the trees that surround you and peer in, cocking their heads inquisitively.
The banda roofs have been specially designed to catch rainwater, which is channelled through filters and into a tank under the floor, then hand-pumped across solar panels into the bathroom. Grey water from the showers is released into sealed flower beds around the outside of the building, containing plants chosen for their ability to take up phosphates and oxides from the soil so that nothing is wasted. The lights are also solar powered, and instead of flushing the loo, a polite notice asks you to throw in sweet-smelling compost ('two scoops') from a handily placed basket.
The upper deck of the banda creaks as you climb the ladder to the bedroom - or rather bed platform. Tiny spots of sunlight filter through the palm thatch of the roof, spangling the white gauze of a huge four-square mosquito net and making patterns across the mattress on the floor. Hooks have been whittled from twigs for your clothes, and shelves are made from driftwood planks, fastened together and suspended from the wall with coconut-fibre rope. Looking out towards the sea, the front wall of the bedroom acts as air conditioning and window combined - lower it with a rope, and you can lie in bed and gaze at the sky. This is state-of-the-art eco-architecture with a touch of salvage chic.
By the time I'd finished scampering round my banda and whimpering with excitement, the sun had come out again and it was time for lunch. There are only seven bandas on Chumbe, allowing 14 guests at a time, so there's no real need for a proper restaurant, just some tables and chairs outside by the sea, and Salim the kindly waiter to bring out steaming pottery dishes of spiced kingfish and coconut rice. Almost all the staff on Chumbe are local Zanzibaris from the fishing community, retrained as 'marine rangers', who spend two weeks on the island and then one week back in their villages, educating their neighbours about sustainable fishing methods. Catches, which have been steadily declining in Zanzibar over the past few years due to overfishing, are reported to be levelling out.