Borkum is the largest of the seven East Frisian Islands by area, roughly thirty-one square kilometres of dune and beach, yet for most of its history it was not one island but two. Westland and Ostland sat separated by a shallow channel until 1863, when natural drift and deliberate land reclamation finally fused them into a single body. The seam still has a name, Tüskendör, "in between," marking the old divide just east of the airfield. Locals say that if you squint at a map, the whole island looks a little like a dolphin. Flat as a tabletop, its highest dunes rise barely six metres, and the persistent westerly wind is the only real obstacle a cyclist will ever face.

Far out in the North Sea, beyond the shelter of the mainland, Borkum catches the full force of the open ocean. The climate here is genuinely offshore, raw and bracing, and the air carries remarkably little pollen. In the nineteenth century, Germans came to believe that air like this could cure what ailed them. Borkum opened as a North Sea bathing resort in 1850 with 252 visitors that first season; by 1900 more than sixteen thousand were arriving each year. Today it holds official standing as a state-approved Nordseeheilbad, a North Sea health resort, and tourism sustains nearly the entire island. The town of Borkum is unusual in spreading across the whole of its island rather than huddling in one corner.

In a chain of car-free islands, Borkum breaks the rules. Along with Norderney it is one of only two East Frisian Islands that permit motor vehicles, though even here cars are kept out of the settlement's heart in summer and banned everywhere from nine at night until seven in the morning. There is another quirk of geography: as the westernmost island in the chain, Borkum is actually faster to reach from the Netherlands than from mainland Germany. Ferries run from Emden and from the Dutch port of Eemshaven, and once ashore an island narrow-gauge railway, the Borkumer Kleinbahn, has been carrying passengers across the dunes for well over a century.

Almost all of Borkum, save the town and the airfield, lies within the Lower Saxony Wadden Sea National Park and the wider Wadden Sea UNESCO World Heritage Site, the largest unbroken expanse of tidal flats on the planet. The island is sliced into three protection zones. The eastern reaches form the quiet zone, where you may walk only on marked paths the year round; an intermediate zone opens outside the breeding season but still gives wildlife the right of way; and the recreation zone takes in the bathing beaches along the south, west, and north. It is a careful compromise between the millions of migratory birds that depend on these flats and the holidaymakers who come for the cure that first put Borkum on the map.

Borkum's position at the entrance to the Ems estuary made it a place that watched the water, and the Old Lighthouse, the Alter Leuchtturm, still stands as a memorial to that vigilance. Generations of pilots and merchants depended on islanders to guide vessels through the shifting sandbanks into and out of one of Germany's busiest river mouths. The same exposed setting that draws health-seekers to the beaches has always made the surrounding sea treacherous for sailors. Because almost everything sold on the island must arrive by the same ships that bring the visitors, prices carry an "island surcharge," a small toll the captive market pays for the privilege of living and holidaying this far out in the North Sea. Borkum has never been an easy place to reach, and that, in the end, is much of its appeal.