The spy who came in from the cold

Unlikely as it may sound, Germany's bleak and chilly North Sea coast somehow inspired the creation of a classic British espionage novel. But did the author know then how significant his story would become?

Next year marks the centenary of an extraordinary novel – the first modern British spy story, and one of the best travel books ever written. The Riddle Of The Sands predicted the First World War; it may have even helped start it. But like all great thrillers, the power of its plot is matched by the potent magic of its setting. When I first read it, I vowed to retrace the eerie route of this intensely atmospheric yarn.

The Riddle Of The Sands is about a pair of patriotic English yachtsmen on a sailing trip along Germany's windswept North Sea coast, who stumble upon a fiendish Prussian plot to invade England. Its author, Erskine Childers, sailed this wild shoreline himself. Although his alarmist story was pure fantasy, its real life locations are charted with navigational precision.

"That district of Prussia which is known as East Friesland... is a short, flat-topped peninsula, bounded on the west by the Ems estuary and beyond that by Holland, and on the east by the Jade estuary; a low-lying country, containing great tracts of marsh and heath, and few towns of any size; on the north side none."

Childers' own life story was as exciting as his fiction. An Anglo Irishman who divided his fervent nationalism between England and Ireland, he fought for King and Country in the Boer War and the First World War, but then sailed to Germany to smuggle German guns to Ireland. After the Great War, he became a brilliant publicist – first for Sinn Fein, and later for the IRA. During the Irish Civil War, he was arrested by the army of the Irish Free State and executed – but only after he'd shaken hands with every member of the firing squad. Half a century later, his son became president of the Irish Republic.

In the turbulent century since his prophetic bestseller, Germany has changed beyond all recognition, but the mysterious setting of Childers' only novel has somehow escaped the tide of history. East Friesia, on the barren shoulder of Germany, is still a place apart – overwhelmingly rural, and unscathed by tourism. It is an isolated patch of land where both Holland to the west and Germany to the east seem like foreign lands.

The irony is that although nowhere in Germany feels further from Britain, this brooding hinterland of dykes, canals and Edwardian espionage is actually the corner of the federal republic that is closest to the UK.

Childers clearly had mixed feelings about this weather-beaten floodplain. He called it "an abominable coast – desolate to the last degree", yet it's obvious he was transfixed by its bleak, unforgiving beauty. He sailed all the way to the West Indies and only wrote a few letters about that voyage. Conversely, he maps this barren scenery in almost obsessive detail. "The atmosphere of grey Northern skies and miles of yeasty water and wet sands is as masterfully reproduced as in any story of Conrad's," enthused John Buchan, author of The Thirty-Nine Steps – a gripping yet far less sophisticated adventure.

One hundred years after Buchan's rave review, you can practically use Childers' novel as a guidebook – so meticulous are his descriptions, and so little has this lonely landscape changed.

Childers' portraits of the East Friesian people are as paradoxical as his landscapes. "They're excellent folk," says his enigmatic German protagonist, "but they're born with predatory instincts. Their fathers made their living out of wrecks on this coast, and the children inherit a weakness for plunder." Yet their great-great-grandchildren have inherited nothing stronger than a weakness for tea. Unlike most Germans, East Friesians prefer tea to coffee, and fish to wurst. They even have their own dialect, more or less incomprehensible to other Germans. And though it's even harder to fathom if you're British, its rhythms sound curiously Anglicised. Instead of "Guten Tag", they say "Moin", which sounds a lot like "Morning"' but it's got more to do with the pitch and tempo of the accent than the words themselves.

Could this be a linguistic echo of the language our German ancestors brought with them? After all, this is where the first Anglo Saxons came from, 1,500 years ago.

My first port of call, like Childers', was the tiny harbour spa of Bensersiel, where boats depart for the remote island of Langeoog when the unruly tides will carry them. In Childers' novel, and in the log of his odyssey that inspired it, locals reacted to his arrival as if he'd fallen from the sky. I didn't receive quite the same reception. Nevertheless, you feel like an adventurer in this monochrome and muted seascape.

A few miles inland is Esens, a cluster of gingerbread houses, huddled around an ornate brick church excessively big and regal for the pretty little market town it serves. From its tower – another of Childers' landmarks – fenland stretches out to the south, west and east, the "great tracts of marsh and heath" that Childers recorded with stark accuracy, halted only in the north by the slate grey frontier of the sea.

Westward is Norden, a far bigger town, guarded by two giant windmills, and built around a huge old square of handsome brick houses. The architecture, like the surrounding countryside, seems more Dutch than German – and with their sailors' caps and bicycles, so do its inhabitants. From Norddeich Mole, Norden's harbour, you can sail to Norderney – the island where The Riddle Of The Sands reaches its exhilarating climax.

Trains run right up to the quayside from as far away as Berlin and Munich, but Norddeich is still a pretty desolate place (especially out of season, when Childers made the trip) and the sea crossing can be equally daunting. Down below, the ferry is warm and cosy – but up on deck the weather can be savage, as the boat snakes a narrow course between deadly sandbanks that have wrecked so many ships before.

An hour later, Norderney looms into view – barely more than a sandbank itself, only a few feet above the water. But after such an intimidating introduction, this nautical hideaway is a very pleasant surprise.

Norderney has only one town, which shares the same name as the island, but its imperial grandeur is out of all proportion to its size. In dramatic contrast to the dark brick houses on the mainland, its smart avenues are lined with elegant whitewashed villas – architectural relics of Germany's affluent, self-confident Second Reich. In winter it's funereally quiet, but the town still gleams in the pale sunlight, as if its neoclassical façades had been scrubbed until they shone. Childers' "great white hotels" are all still there, and so is his "gorgeous casino". Even the municipal post office looks more like a metropolitan town hall.

Norderney is the second largest of the seven East Friesian islands. Even so, it is only seven miles long, and barely a mile across. Cars are confined to the town, at the western end of the island, and the only way to see the eastern end is by bike, or on foot. Cycling east, you soon become lost in a maze of sand dunes, flanked on both sides by miles of brilliant white beaches, battered by a restless sea.

From the lighthouse at the island's core, you can see out to sea in both directions – southwards towards the mainland, northwards into the cold wide "Nordsee", and not another soul in sight.

I caught the southbound ferry back at sunset. As the sun sank into the icy water, the horizon turned from grey to silver, and Norderney faded into a faint mirage, floating between sea and sky. As the ship slid between two sandbanks, I thought I saw a crowd of corpses – the drowned bodies of shipwrecked sailors, washed up on this shifting shore. And then I realised they were seals – watching us sail past, just like they'd watched Erskine Childers sail past a century earlier.

If Childers has a ghost, he is still haunting these weird waters. It is hardly a typical holiday destination, but it's one of the most arresting places I've ever been.

When I got home, I read The Riddle Of The Sands again – but to my surprise, the pictures in my head had scarcely changed. Usually, when you read a book that's set in a place you've never seen before, your mind's eye creates a landscape utterly at odds with reality. Yet this time, my imagined landscape and the real one were virtually the same. Childers didn't just describe this "abominable coast" – for his readers, he created it. And revisiting it, a century later, you become a ghost yourself, as you relive his maritime memories, and step inside the imagination of a man who's been dead for 80 years.

William Cook travelled as a guest of Lufthansa, Deutsche Bahn and the German National Tourist Office

Traveller's Guide

Getting there: to follow in Childers' wake, from April DFDS Seaways (08705 333 000, dfdsseaways.co.uk) will sail from Harwich to Cuxhaven, at the mouth of the Elbe estuary. (The Riddle Of The Sands actually begins in the Dutch port of Flushing.) The quickest way to the Friesian Islands is by plane and train. The nearest airport with direct flights from Britain is Bremen, with three flights a day on British Airways (0845 77 333 77, www.ba.com) from Gatwick. Fares are likely to be lower to Hamburg or Hannover, both of which are served from Britain by BA, Lufthansa (08457 737 747; www.lufthansa.com) and Air Berlin (0870 73 88880, www.airberlin.com).

From any of these cities, you can travel by train to Norddeich Mole – the return fare from Hamburg or Hannover is around €50 (£35), about half as much from Bremen.

A scenic alternative is to take a train from London or Ashford to Brussels, change there for Amsterdam and continue to Groningen. This will cost £85 return through Eurostar (08705 186 186, www.eurostar.com), or £145 return in first class. You then need to travel across the border to Leer, and change again for Norddeich. The ferry from Norddeich Mole to Norderney costs €13 (£9) return.

Staying there: rooms at the Reichshof Hotel Norden (00 49 49 311 750; www.reichshof-norden.de) cost €53 (£32) single, €96 (£64) double, including breakfast. Insel Hotel Vier Jahreszeiten Norderney (00 49 49 328 940; www.norderney-hotels.de) costs €62 (£42) single, €70 (£47) double, including breakfast, in January. For more information, contact the German National Tourist Office (020-7317 0908; www.germany-tourism.de). If you read German, you could visit www.norderney.de or www.bensersiel.de.

Simon Calder