To stand at the top of the near-sheer cliff that vanishes into the Aegean is to feel you are on the edge of disaster. Wintry clouds glower darkly, while slick, black rocks usher your eye down to the surf crashing with fury and futility against the western shore.
Let your gaze follow the white-flecked crescent of coastline and, when the land ends, allow your imagination to complete the circle, as it might a young moon. The lunar analogy is apt, because looming from the sea are heaps of debris straight from the Nasa props department. The word "calamity" is barely appropriate for what happened here.
There came a sound, as if from within the earth
Zeus's hollow thunder boomed, awful to hear.
The horses lifted heads towards the sky
And pricked their ears; while strange fear fell on us
Euripides was writing five centuries before Christ, but the event he was quite possibly describing happened at least a millennium earlier. At some fateful instant between 1500 and 1625BC, the always abrasive plate tectonics of the eastern Mediterranean climaxed in a catastrophic eruption that tore the core from an island the size of the Isle of Wight. It wasn't the Atlantis of myth, but it was a thriving community.
When you survey the surviving fragments of one of the biggest volcanic eruptions in the past 10 millennia, you feel in alarmingly close contact with the earth's crust. Present-day Santorini (also known as Thira) comprises a scattering of crumbs only tentatively attached to the rest of the planet.
The impact of the erupting volcano changed the ancient world, but in Greece there is clearly no such concept as seismic blight; even though little remained beyond a semicircle resembling a half-submerged Olympic ring, man clawed his way back on to the largest surviving fragment of the island. Santorini has found a post-apocalyptic role as a community dependent on agriculture and tourism.
Climb the highest point of the island - Mount Ilias, around 600 metres above the simmering sea - and you can see how scruffily the repopulation has sprawled across the eastern slope.
Luckily, Santorini's main town, Fira, embraces all the values of an idyllic Cycladic settlement: a mix of delicate white cottages on the crest of the caldera, laced with narrow lanes that resonate with church bells. In summer, torrents of tourists swirl through the town, but in midwinter your only company is likely to be a community of funny little cats.
Your problems, meanwhile, are likely to be considerable. The good thing about the Greek islands out of season, it is commonly said, is that they are wonderfully quiet. That inoffensive word "quiet" conceals a consensus of closure, the concept that an entire island can be operated on a skeleton staff. The Volcano Hotel, the Atlantis restaurant and the Enigma disco are all shut down, as are almost all of the "rooms" that cater for the summer's flotillas of backpackers.
Furthermore, the weather is frequently foul. I am staying at the ambitiously named Porto Fira Hotel, which resembles a warren of white-washed Hobbit holes. The rain has been bombarding for a couple of days now, splashing against the whitewashed walls. Every so often the grey is enlivened by a flash of lightning that heralds an Atlantean rumbling of thunder. The electric heater in the room has just fused after I tried to dry my sodden socks on it. At 2am last night, the only surviving mosquito in the northern hemisphere managed to insinuate itself into my room, despite the door and window being sealed against the cold, and dined famously.
Now and again, though, the sun emerges and makes it all worthwhile, when shafts of gold light play poetically upon the ragged wilderness. And, if you meander along to the patch of ground that serves as a bus station, you can travel around the crescent of Santorini to a place where the solitude of winter is rewarded.
You know Pompeii? Imagine a city twice as old, which suffered the same volcanic smothering but is preserved even more perfectly. You may doubt this when the bus-driver drops you off by a iron gate in the far south west of Santorini. But persevere: wander into a field with a smattering of buildings and, beyond, you find a slender ravine covered with brutish corrugated iron. This ungainly roof serves as insulation for the miraculous resurrection of life in the second millennium BC.
Four or five thousand people lived in Akrotiri before the eruption. They were accomplished mariners, which provided them with both wealth from trade, and ideas from ancient Egypt. Nearly 4,000 years ago their city was accomplished in its technology - the walls of two- and three-storey buildings bear witness to advanced engineering - and its artistry, with vibrant wall paintings and elaborate pottery depicting a sophisticated society.
The art has been appropriated by Athens, and you will need to visit room 48 of the National Archaeological Museum in the capital to gasp at the intense images. But the fortunate winter visitor may encounter Professor Christos Doumas, who has been excavating the site for three decades. As you wander around streets whose tangle mimics the modern-day town, he will explain yet more similarities to the 20th century: how certain buildings served as shops and banks to a busy, wealthy community. And he will point out the grave of Spiridon Marinatos, the man whose meticulous research led him to uncover Akrotiri beneath many metres of volcanic dust in 1967. Professor Marinatos died in a fall at the site in 1974.
Intriguingly, his is the only human corpse known to exist in Akrotiri. The citizens appear to have been fully aware of the vulnerability of their location. It appears that before the eruption they fled the city, thoughtfully leaving jars full of grain beneath doorways - then, as now, this was the safest place in an earthquake.
Just as a door frame could not withstand the weight of tons of volcanic ash, so there remains no trace of the population ever having made safe landfall, given the scale of the tidal wave that accompanied the eruption. Euripides again: To the sea-beaten shore/ We looked, and saw a monstrous wave that soared/ Into the sky.
The reverberations of the volcano are still being felt. Last century, for example, the French engineer Ferdinand de Lesseps used volcanic ash quarried from Santorini to make the impervious concrete essential to the building of the Suez Canal - a fundamental artery for the modern world.
Back on the island, though, there remains one more ritual for the winter visitor. If you can gather together a few stragglers left over from the summer season, you can charter a fishing boat for about pounds 50 from the timid little harbour that huddles at the foot of the cliff. From here, you can appreciate the wide-screen wonder of the rock face, and discern many more colours than the black that first registered, with electric greens and rust reds prominent.
The boatman will steer out across the submerged crater, towards a recent creation: the island of Nea Kameni ("new burnt island"), directly above the centre of the crater. It has emerged over the past three centuries, but fits no preconceptions of what a Greek island should look like; the earth has simply spewed volcanic wreckage into the Aegean, with the lava freezing where it fell.
Talking of freezing: if you are feeling brave, or foolhardy, or working for a radio producer keen on some audio verite, you may plunge from teh boat into the wintry water and paddle frantically around in search of the promised 40C currents.
The sulphuric steam rising from the centre of the island draws you along a narrow inlet, and reminds you of Euripides's "foaming blood and breath from the deep sea". But soon the crush of rocks gets too intense and you retreat to the cooler, choppier Aegean, where you can reflect on the fascination about Thira that goes way beyond its rugged beauty - a place where history meets hydrodynamics, vulcanology meets archaeology, and science meets fiction.
Gazing at the destruction poses some big questions. Where and when will there next be an eruption of such magnitude? Could Thira itself ever change the world again? And where's that towel?
Getting there: Simon Calder's ticket - from London via Athens to Santorini, with a side-trip to Crete - cost pounds 359 on Olympic Airways (0171-409 3400).
Once the summer flights begin and the ferries start a more regular service, it will be much cheaper to reach the island. The peak-season alternatives are as follows:
(1) Taking a scheduled flight from London to Athens on British Airways (0345 222111), Cronus Air (0171-580 3500), easyJet (0870 6 000 000), Olympic Airways (0171-409 3400) or Virgin Atlantic (01293 747747), followed by a ferry from Piraeus.
(2) The same idea but using a charter from a range of UK airports to Athens.
(3) A charter flight to Heraklion, on Crete, and a ferry from there.
(4) A direct charter flight from Gatwick to Santorini, perhaps as part of a package; Kosmar Holidays (0181-882 6999) is one of relatively few companies to go there, starting in May.
Getting around: Bus services around Santorini operate year-round, with a maximum fare of about pounds 1. Car rental is cheap and widely available. Cycling is not a happy way to travel around the island in winter.
If you plan to visit Santorini as part of an island-hopping itinerary, then Greek Island Hopping 1998 by Frewin Poffley (Thomas Cook, pounds 12.95) is the essential survey of all ferry services plus entertainingly pithy descriptions of the islands. The 1999 edition (same price) will be published on 12 March.
More information: Hellenic Tourism Organisation, 4 Conduit Street, London W1R 0DJ (0171-734 5997). A good source of books is Hellenic Bookservice, 91 Fortess Road, London NW5 1AG (0171-267 9499).
`The Volcano That Changed the World', presented by Simon Calder and produced by David Sharp, will be broadcast on BBC Radio 4 at 8pm next Thursday, 4 FebruaryReuse content