As we are now entering the "magic tunnel", Rob - our tour guide - tells us coach-load of sceptical holidaymakers: "It may look dull and overcast here, but when the coach emerges, the sun will be shining."
Pull the other one. For days a pall of mist has hung over our walking trip to La Palma, the most north-westerly of the Canary Islands, broken only when we rose above the cloud line on the rim of the island's highest volcano.
But Rob is right: astonishingly, there is, quite literally, light at the end of the short - 1,100m - tunnel. The sky is blue and the sun is blazing.
The dramatic weather change is just one of many contrasts we witness in our week on this small but surprisingly varied island.
On a heart-shaped piece of land no bigger than Anglesey, we trudge through snow and bask on black sand; walk through lush forests and across barren lava fields; pick our way down a mule track and window-shop on a sophisticated Spanish high street.
Getting there
Package: HF Holidays is offering a seven-day guided walking holiday on La Palma including flights, transport and en-suite half board accommodation at the Parador de la Palma from £949 per person.
The world's steepest island - it is impossible to move more than a pace or two on La Palma without either climbing or descending - is perhaps not the obvious place for a middle-aged novice to test her walking abilities. And my anxieties are not alleviated by the first night's health and safety talk.
"If you become separated from the rest of the group, stay where you are and make as much noise as possible," advises our guide Peter, a retired RAF engineer with the build of a whippet and the sure-footedness of a mountain goat. "And remember to carry plenty of water. Dehydration can be fatal."
The week's high point - literally and metaphorically - is a walk along the rim of the Caldera de Taburiente, once believed to be a vast volcanic crater but actually a semi-circular ravine 8km across and up to 2,000m deep.
Below us there is cloud - dense and inviting as a cotton wool bed - a sight normally seen only from an aeroplane. By our side, the jagged black teeth of the 2,350m high Pico de la Cruz pierce the whiteness. Ahead across the sea, the peak of Teide on Tenerife, her flanks draped in snow, rises out of the mist like a Greek statue guarding its modesty. As we trek across the snow in a silence broken only by the occasional chirrup of an insect, the world seems a million miles away, the landscape almost lunar.
A raven visits us at lunch, a raptor soars overhead, and occasionally we step aside to allow a Lycra-clad mountain runner to sprint past at improbable speed like a gazelle in racing colours. Otherwise, we are alone.
The other-worldliness deepens as the golfballs of the Roque de los Muchachos observatory pop into view.
Conditions on the Caldera make it among the very best places in the world to explore the deepest reaches of the universe.
Among the bank of telescopes is the Magic (yes, there's more than one kind of enchantment on this island), a massive concave mirror searching space for dark matter.
Together with Tenerife, La Palma is the most volcanically active of the Canary Islands with seven eruptions since the Spanish occupation in the 15th century, the most recent in 1971.
Reassuringly, none were especially devastating, but there is no escaping their effects.
At Fuencaliente - the name means warm spring, but the source was buried in an eruption - we cross the southernmost lava field of the Cumbre Vieja (old summit) ridge that runs like a spine down the centre of the island.
Every kind of lava crunches beneath our feet from the fine ash or picón on which flourish the distinctive creeping vines of La Palma to larger coals and rubble-like boulders.
This is not a monochrome landscape. Small plants of an almost fluorescent yellow-green make the wilderness resemble a garden.
And lava itself is not uniformly black, but shot through with streaks of rust red, orange and even cream.
In fact, the whole island is splashed with colour. Houses painted pistachio, vermilion, citrine and terracotta, verdant forests and lush banana plantations stand out against stark hills, ravines and valleys.
A striking contrast hits the eye as we descend to sea level and see below us the red and white stripes of the Fuencaliente lighthouse and beside it, the checkerboard of the salt pans.
These produce half a million kilos of salt annually through evaporation of sea water through a series of pools. The product is deliciously delicate, but sadly, not available in the UK.
Another walk takes us through the "magic tunnel" to the sunnier west side of the island. Here we follow old mule paths through precipitous gorges above a cobalt sea from Tinizara to Tazacorte. Rob points out edibles - including loquats, custard apples and prickly pear - and birdlife: wagtail, blue tits and - yes - a canary. A kestrel sweeps above us. The day finishes on the black sand beach of Puerto de Tazacorte, a tiny resort backed by brilliantly-coloured houses and fringed with dark hills.
By the end of the week I am exhausted but exhilarated. Every night I devour the wholesome three-course meals provided by our hotel, the Parador de la Palma (there is always a fish option) and sleep deeply in my room overlooking the Atlantic.
