It's a good pub quiz question: where in Britain can you walk from one coast to another in just four hours? Thanks to a deep incision of the Fal estuary, the answer can be found in west Cornwall, where 11 miles separate the muddy creek at Devoran on the south coast from the sands and waves of Portreath on the north coast.
The going is easy too. For the most part, the path is a legacy of Cornish mining that cuts inland from both coasts along old tramways and rail lines.
At Devoran it is low tide as I set off, and the centuries-old imprints of tramways sink magically into the water. The idyllic creek is a winter haven for black-headed gulls, while the hedgerows sprouting on the lip of the mudflats are all mixed up: their tangle of elevated roots, as if on stilts, recalls mangroves from more exotic shores.
Turning north, I pass the old workshop of the 19th-century Redruth and Chacewater Railway, reckoned to be Cornwall's first railway. In 1838 Devoran was Cornwall's busiest port, with schooners, ketches and lighters crammed five abreast, stuffed with copper ore and tin ingots, vitriol and arsenic, all key to an industrialising Britain and expanding empire.
Cornish mining has added words to the English language, such as wheal (a mine working) as well as shaft (Cornish for "vertical tunnel"). The industry sent the county's miners to six continents, hence the phrase "go down a mine anywhere in the world and you'll find a Cornishman". Six million people overseas, say the staff at the world heritage site for the area, are thought to be descended from migrant Cornish mine workers.
The tin and copper boom couldn't last for ever, and as prices plummeted, the Devoran line was wound up. What's left behind is the littered legacy of fragmented engine houses, chimneys and lonely arches fronting air. Today, pretty much everything you look at is history. Recently, high global prices for metals and minerals spurred prospectors to invest in some of these mines, hinting at a more optimistic codicil to the tale of tin.
The fixtures and fittings of this walk are contradictory: fractured buildings and forbidding notices warning of ponds and lakes historically polluted by copper-rich mining detritus and spoil tips. Yet the miniature river Carnon to my left is picturesque and I'm struck by the unusual sensation of looking upwards in Cornwall. This is the county of coastal walks, where we rush through the landscape on the elevated A30. But here, deep in the Carnon valley, I am surrounded by gentle heather-clad hills and overlooked by Brunel's striking arched Carnon rail bridge, which still supports the branch line from Truro to Falmouth.
And the landscape is quirky: the valley cuts at right angles to the veins, or lodes, of minerals that were excavated, and helpful interpretation boards create the impression of an open-air geology lesson. To my right, reedbeds are home to blue-tailed damselflies, frogs, toads, snipe and moorhens. Those polluted valley ponds are steadily cleaning themselves, while only hardy mosses and liverworts – little changed since they appeared 400 million years ago – can thrive in these nutrient-poor soils.
On the skyline a lean-to chimney stack heralds the halfway point of the walk. For a few minutes, as I squeeze along narrow pavements, wincing from impatient drivers, the walk is tedious. More enticingly I then take the road bridge over the A30 past the front door of Rodda's cream factory. Close by, at the back of an unpromising industrial estate is a superb pasty shop. Uplifted, I am quickly thrown back into a rural Cornwall. This northern section is quieter and bucolic, a rolling hinterland of hedges, farms and good farm shops.
As I approach Portreath there are views of the Carn Brea monument, a landmark visible for miles across Cornwall. A gloriously shaded path of hornbeam pollards accompanies me into Portreath where the wind is sweeping the waves up the beach. I sit on the sea wall, adjacent to a large, all-but-empty car park.
Later I visit the nearby Poldark mine, whose heyday lies deep in the 18th century. I discover the name was simply a shameless 1970s marketing ploy linked to the novels of Winston Graham. Nevertheless, Poldark is charming and informative, and the authentic if slightly hair-raising underground tour puts the romance in context: mining meant close-knit communities, the chance of a modest fortune, but also a dismal accident rate and child labour.
I root around for an ice-cream shop open out of season, and speak to Ainsley Cocks of the Cornish Mining World Heritage Site, whose passion for Cornwall borders on the evangelical. "If you like walking, when you come to Cornwall you will encounter the mining heritage at some point," he booms. "Many people think of Botallack, of fantastic, precarious locations by the coast, but there is a lot more to it – the mining towns and settlements, the tramways that connected the inland mines to the coast, the tin smelters, the iron foundries. You get a feel for the mining landscape and its place in the world."
Map OS Explorer 104 Redruth and St Agnes
Distance 11 miles/19km
Time Four to five hours
Route The route from Devoran to Portreath (or in reverse) is straightforward and well waymarked with blocks of granite imprinted with the image of engine houses. The route is a shared path, and walkers can expect to encounter horses and cyclists.
Mark Rowe stayed at the Retallack Resort (01637 882400; retallackresort.co.uk) near St Columb where two-bed chalets start at £209 for a three-day stay, rising to £1,299 per week in high season.
Cornish Mining World Heritage Site: cornish-mining.org.uk
Poldark Mine: poldark-mine.co.uk