Well, for the denizens of sweaty Lisbon, 20 miles down the road, this mist has long had its attractions. Just as the British Raj trooped up to Simla during hot summer months, so Lisboan aristos have traditionally retreated to Sintra. And mist makes this precipitous hill town beautiful, as the turrets and spires of the castles and convents become intermittently visible through the trees. Its celebrated Cork Convent - so deeply buried in foliage that the sun never penetrates - would make the perfect setting for Giselle; and its equally celebrated Monserrate gardens - laid out two centuries ago by the novelist William Beckford after he was drummed out of Britain for sodomy - would make an ideal backdrop for A Midsummer Night's Dream.
But when the mist does clear, what a place. Glorious Eden, said an ecstatic Byron, who sat here writing Childe Harold. The town itself is a maze of narrow streets hugging the contours of the hills which rise steeply in every direction. Its centre, which no war has ravaged, is a perfectly preserved 18th-century time-capsule dominated by a medieval palace with eccentric conical chimneys.
The Moorish castle on the nearest crag looks only a short step away, but when we plunge into the forest to get to it we find we're in a maze, since the beautifully kept paths are unsigned. Beyond that, a further maze leads us to a palace reminiscent of mad King Ludwig's in Bavaria - and indeed, it turns out to have been designed by an architect from the same crazy school. Where else would you find a sundial in the form of a cannon timed to fire at noon? At least here - above the clouds - the sun really does shine. Meanwhile, from below, we hear unearthly wails: Formula One cars at Estoril.
Wherever we walk in these forests, we get tantalising glimpses of gorgeous mansions behind locked gates: a lot of rich celebs lurk here, escaping the glare. One gate which is open leads to a turn-of-the-century folly of jaw-dropping extravagance. The Quinta da Regaleira was created for a Portuguese Midas by an Italian stage-designer, but the grottoes and tunnels in its gardens seem like the set for a Spielberg fantasy.
Passing the Casa O'Neill - not open to tourists, but the place where Hans Christian Andersen stayed in 1866 - we persuade the owner, a retired professor called Germana Tanger, to let us look round. It's a delightful little cottage, and would well have suited the neurotic Dane, whose terror of being trapped in a burning upper room led him to carry a length of rope wherever he went. I can sympathise with the professor's excitement as she points out the bits which have remained unchanged. "At this point here," she says, standing starry-eyed by the door, "I feel a strong spiritual presence." The Hans Christian Andersen Society, she adds, makes regular pilgrimages.
Meanwhile, the Byron Society is champing at the bit, because Lawrence's - the hotel where the poet stayed - has just reopened after lying derelict for 50 years. And what's more, in as close an approximation as possible to the state it was in when Byron knew it. The Dutch owners Jan and Coreen Bos have spent 10 years researching everything from decor to building design, and the result - overlooking a leafy valley - has exquisite period charm.
"The Byron Society wanted a plaque put up in the room where their hero stayed," says Jan. "But I refused. This place is about life, not death. But they're welcome to stay here." And eat here: the cuisine is top-rank Portuguese, but the Bos trump card is the English cookbook used by the first Mrs Lawrence, from which one dish each night is taken. I rather fancy the one headed "To bake a pig", which begins: "Wash the pig very nicely, rub it with butter, flour it all over", and concludes: "Send it up in a tureen." Incidentally, the waiter by whom it would be sent up worked here as a boy 50 years ago: typical of Sintra's serene continuity. On the other hand, Jan has been told he'll have to wait a year to register his phone number: if you need to earn a living, this serenity can be maddening.
Sintra's recent designation as a Unesco World Heritage Site has given it new muscle to fend off the developers. Mario Machado, born and bred there and now running the tourism office, says with feeling: "We don't want mass-tourism, we want visitors who fit in." So young ravers, please note. Having seen his little town choke to death under the onslaught of bus and car, he's now managed to reverse the tide, by keeping vehicles penned up in the "new town" across the valley.
Talking of cars, we quickly learn to avoid the motorways - abominably signed and full of mad drivers - and stick instead to the leafy lanes, along some of which there are rails. One of Sintra's latest wheezes is the renovation of the old American tram system which now runs straight down to the sea. And for a trip into Lisbon, we find a neat little Japanese train which takes 40 minutes and lands us in the middle of town.
But why leave Sintra, when the place has so much to offer? For example, a toy museum like no other in the world has just opened there. Its owner, Joao Arbues Moreira, has gone for what he calls "toys with history", and the history reflected in this collection is indeed arresting. The charming doll's-houses go back centuries, as do the tin soldiers, but the 20th-century combatants with their guns and field-hospitals reflect Portugal's close German links: here is Hitler taking the salute with Himmler and Goering, and there, a fleet of German tin battleships from the First World War. Moreira's passion for cars reveals itself in thousands of Dinky toys, and more seriously, in some big Bugattis and Ferraris, and in the foot-long Citroens which that company used in the 1930s as a bait to snare buyers through gifts to their brats.
And look at all that art. The casino has been transformed into a gallery which almost rivals the Tate. Named after its founder Jose Berardo, it offers a chronological view of 20th-century art, but the works have been selected with an unerring eye. We find charming period kitsch at the gypsy-dominated Feira da Ladra, which blossoms on Sunday morning in San Pedro square. And coinciding with the annual music festival, we get concerts every other night, for which the palaces make stunning venues. A glorious Eden indeed.
SINTRA AND THE DOURO VALLEY
Martin Symington travelled with GB Airways (tel: 0345 222111), which flies twice daily from Gatwick to Oporto. Apex return fares cost from pounds 138.50 including taxes. Go (tel: 0845 6054321) flies daily to Lisbon from pounds 90 return. Simply Portugal (tel: 0181-987 6161) offers one-week fly-drive holidays, with b&b accommodation from pounds 495 per person, based on two sharing.
WHERE TO STAY
Sintra: For quiet efficiency in a central location, go for the Tivoli Sintra (tel: 00 351 9233505). For eccentricity, stay at the Solar dos Mouros (tel: 00 351 9233216). For sheer magnificence, at a price, get a Napoleonic berth at the exquisite Seteais (tel: 00 351 9233200).
Douro: Good accommodation is hard to find in the Douro valley. But a beautiful, four-star hotel opened recently in Taylor's former quinta house at Pinhao. Vintage House Hotel (tel: 00 351 54730230) charges from Es15,000 (about pounds 60) for a double room. From Pinhao, Tua is 15 minutes by train and Pocinho about an hour.
THINGS TO DO
You must make an appointment to tour the Foz Coa Archaeological Park. Apply in writing to the Parque Arqueologico Vale do Coa, Avenida Gago Coutinho 19, 5150 Vila Nova de Foz Coa, Portugal (tel: 00 351 079764317; fax: 00 351 079765257; e-mail firstname.lastname@example.org.). Tours are for up to eight people in a 4WD. They last about two hours (in English, French or Portuguese) and leave from the visitor centres at Vila Nova de Foz Coa, Muxagata and Castello Melhor. A token Es500 (about pounds 1.80) per person is charged. Otherwise, you can visit the valley through Ramos Pinto, including a visit to its museum at Ervamoira in the Coa valley, and a wine-tasting. Transport from Pocinho station can be arranged and lunch provided by arrangement. Contact Sonia Teixeira (tel: 00 351 079 759229).
From the Portuguese Tourism Office (tel: 0171-494 1441).Reuse content