Next day, things get more Indiana Jones: Luis Mario announces an all-day hike through the rainforest. With his machete, he slashes a trail through loops of liana. Monkeys swing high in the canopy, and Luis highlights vibrant yellow-breasted weavers and giant begonias.

'It looks pristine,' he explains, 'but all this is actually secondary rainforest that has taken over from the plantations which once covered these mountains. When I was a child and my parents worked here, it was all cultivated.' Reforestation it seems, rather than the reverse, is São Tomé's problem. There are glimpses of orange-brown cocoa pods hanging from bushes amid the undergrowth; but rather than harvest them, young foragers encountered along the way prefer to tap palm trees, filling jugs with the sap for fermentation into head-swimming palm wine.

'There are no jobs for young people in São Tomé,' explains Luis. 'They think that money and work will come from the oil companies.' Oil has been found in the Gulf of Guinea and an exploration deal signed with Nigeria, but for Luis, the future is more likely to be in tourism: 'We have so much natural beauty,' he gestures.

The hike comes to an end near the tiny settlement of Batepá, the scene in 1953 of an atrocity that left a stain on the reputation of the Portuguese colonials, auguring their ultimate downfall. Hundreds of workers, protesting against conditions of virtual slavery, were shot dead by the militia. Antonio Nunes, a former worker, remembers it all too well: 'My uncle was killed, my brother wounded. The shooting continued for days.'

Photos of bullet-ridden bodies record the extent of the atrocity at the National Museum in the 16th-century fortress of São Sebastião. They are arrayed alongside a silver salver presented to the Portuguese governor the previous year, apparently by the very workers who perished. There is more to stop visitors in their tracks: among the weirdest exhibits is the remains of José Ferreira Gomes, who introduced the cocoa plant from Brazil to São Tomé and Príncipe in 1822.

His appropriately chocolate-coloured skull and bones lie in a satin-lined wooden chest like some extravagant Halloween box of tricks. Cocoa was planted initially on Príncipe, one-third the size of its sibling and reached on a 45-minute flight aboard Air São Tomé e Príncipe's 17-seat Twin Otter propeller plane. We circle over sugarloaf lumps of greenery and opalescent coves, putting down on an airstrip next to Roça Sundy plantation, where the first crop took hold.

It is among a selection of crumbling plantation houses currently under restoration, Bombaim-style, for 'rural tourism' on Príncipe. On completion, rooms will command dramatic views over mountains and ocean. When guests tire of doing nothing, there's a whole island to explore: from Roça Sundy, a red-dirt track snakes through thick forest across the island to Santo António, the island's 'capital'. It is, in fact, no more than a ghostly village around a neglected square, where schoolchildren play under a fading mural. An avenue of ruined colonial houses is cut through by the River Palhota, and in it women stand knee-deep, soaping clothes and slapping them on black rocks.

But for many new arrivals, indolence will be the order of the day. And who can blame them, with the likes of Bom Bom Island Resort on offer? The most exclusive, expensive hotel on either island, it is a scattering of 25 air-conditioned rondavels beside a beach hemmed with fan palms and banana trees. A walkway crosses to a tiny islet where a restaurant and bar are hung with trophy sailfish and marlin. It all belongs to a South African multi-millionaire who wanted somewhere far-flung and whimsical to indulge his passion for game fishing. Freshly landed barracuda and bonito are served for lunch and dinner, although none of the guests on this visit seemed interested in angling.

Most seem more preoccupied with the beaches, which epitomise paradise-island reverie. Lapping a headland, the shallow water is as clear as a paperweight embedded with shells and pebbles, and I lose count of the time I spend snorkelling among beautiful explosions of searing-yellow grunts and pink-and-blue parrot fish. The past may have been imperfect for Africa's forgotten twin islands, but from this idyllic perspective at least, the future's bright.

Getting there

TAP Air Portugal (0845 601 0932, www.tap-airportugal.co.uk) flies to São Tomé from Heathrow, via Lisbon, from £674. BA flies from various regional airports to Heathrow from £65.

Tour operators

Idyllic Islands off Africa (01993 773269, www.africanislands.co.uk) tailor-makes itineraries. A week's tour of São Tomé staying in four-star hotel Miramar in São Tomé town, the Pestana Equador Resort on Ilhéu das Rolas and Roça Bombaim, costs £1,228pp based on two sharing. The price includes flights to São Tomé from Heathrow via Lisbon (return flight via Sal, Cape Verde and Lisbon), transport, a guide, an all-day rainforest trek and B&B accommodation. A two-week tour, taking in flights to and from Príncipe and four nights at Bom Bom Island Resort, is £2,445pp.

Getting around

Navetur-Equatour (00 239 222122, www.navetur-equatour.st), in São Tomé, organises transport, guides and accommodation.

Further information

Visas and a Yellow Fever certificate are required. Travellers from countries without a São Tomé consular service, such as the UK, can buy a visa on arrival for £34. Malarial prophylactics are essential. The best guide is Gabon, São Tomé and Príncipe (Bradt Guides, £13.95).

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