The glug-glug of bubbles on the surface is a sign of divers in the depths. I watch their dark shapes rippling slowly in the emerald water for a while, before taking a slippery slate staircase winding up through the still autumnal oak woodland surrounding the flooded Vivian quarry.
In a clearing lit briefly by November sun, a brown-coated, blacked-headed beast with horns as magnificent as any fairytale faun, is munching grass next to an old red-painted winding house. It is a scene of storybook strangeness. The horned head turns slowly, fixing me briefly with a pair of yellow eyes, then returns indifferently to its business.
To me the feral goats of Wales seem quite wondrous, a remnant of the Neolithic, but they suffer from the “nuisance” stigma, and in the past have been subject to culls or killed for sport. I have some sympathy for conservationists guarding rare arctic alpines in Cwm Idwal, less for horrified home owners in Nant Gwynant protecting their petunias.
On a broader level, however, if grazing by a few hundred of these shaggy creatures is so damaging, what does that say about the policy of publicly subsidising countless thousands of sheep to chomp the hills of Eryri bare?
I carry on upwards, into the epic surroundings of the main Dinorwic quarry. Two centuries of slate extraction came to an end in 1969, leaving behind a hole half the size of a mountain and some astonishing industrial archaeology.
The vast dry stone constructions supporting the funiculars used to transport the slate have the aura of ancient monuments; under a sky of scudding clouds, these could almost be the echoing remains of some abandoned Andean city.
These quarries now host hundreds of climbing routes, on rock that can be as sleek and frictionless as a blackboard. At first glance, Llanberis slate is a gloomy grey, but closer inspection reveals rippling, pulsing, iridescent veins of purple and green.
With sun showers drifting through, drenching and lighting the sidings, spoil heaps, slabs, derelict buildings and crumbling terraces, it is a kaleidoscopic display of black magic, and a reminder that forms of brilliance can be found even in the heart of winter’s darkness.
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