The festival ran from 4 to 6 September 1970 and drew around 25,000 people to a coastal field in the island's southwest corner. Friday brought storms and unbroken rain. Saturday stayed cold and windy and then rained again. Overnight before it began, 180 members of a Hamburg motorcycle gang, the Bloody Devils, rode up, extorted free fuel from a filling station at Gremersdorf, and brawled in Petersdorf, leaving four Iranian students with knife wounds. The organisers had hired some of them as security; eventually they simply paid them to leave. Sunday finally came up clear and sunny. Then, at around a quarter to eight that evening, the organisers vanished with the day's takings, five hundred unpaid volunteers realised what had happened, and the festival site caught fire. Police restored order to the ashes. A memorial stone stands at Flügge Beach, and from 1995 to 2010 the island held an annual Jimi-Hendrix-Revival-Festival in September.

The island's name is older than any of that and considerably plainer. It comes from the Polabian Slavic fe more — in the sea — sharing its root with Pomerania, po more, at the sea. Fehmarn was settled in the early Middle Ages by the Wagri, a Lechitic Slavic tribe, and marks one of the westernmost points of the once-continuous Slavic settlement zone in Europe. The evidence is still on the road signs: Bannesdorf, Dänschendorf, Gollendorf, Klausdorf, Lemkendorf, Sahrensdorf, Vitzdorf, and a dozen more. Puttgarden comes from pod gard, beneath the castle. German and Danish colonists arrived from around 1200 onward, and the Slavic islanders were gradually Christianised and absorbed. Fehmarn belonged to the Danish Duchy of Schleswig until 1864, when Denmark ceded it after the Second Schleswig War; Schleswig came under full Prussian rule after the 1866 Austro-Prussian War — which is why the island's emblem is still a golden crown on a blue sea, a nod to the Danish royal house of Oldenburg.

Fehmarn covers 185 square kilometres with 78 kilometres of coast and about 13,000 residents, making it Germany's third-largest island after Rügen and Usedom. It is also flat: the highest ground, the Hinrichsberg, manages 27.9 metres. What it lacks in relief it makes up for in light. In 2008 the German weather service recorded Fehmarn as the sunniest place in the country, averaging 4.8 hours of sunshine a day, and the nickname Sonneninsel has stuck. Reliable wind and shallow water have made it one of northern Europe's better windsurfing and kitesurfing destinations, with more than ten known spots. Migratory birds treat the coastline as a rest stop, and NABU runs a conservation centre at the Wallnau waterbird reserve. Islanders play Scharwenzel, a team card game at least three centuries old that is played nowhere else on earth.

Not all the island's history is holiday reading. On 26 July 1932 the German navy's sail training ship Niobe was caught by a sudden squall off Fehmarn's north coast and capsized. Sixty-nine people died. She was a training ship, and the loss was felt across the German navy for a generation. The Niobe-Denkmal at Gammendorfer Strand looks out over the water where it happened. Fehmarn was also, for a few summers, a retreat for Lina Heydrich, who was born in the village of Avendorf and whose husband Reinhard was among the principal architects of the Holocaust. She kept the family's summer house here and ran it as a restaurant after the war until it burned down in February 1969. The island does not advertise this. It is part of the record all the same. Earlier and gentler: the expressionist painter Ernst Ludwig Kirchner spent stretches of the years from 1908 onward working on Fehmarn, and the church of St Nicholas in Burg holds a baptismal font dated 1391.

Everything on Fehmarn eventually comes back to the crossing. Since 1963 the Fehmarn Sound Bridge has tied the island to the mainland, and at Puttgarden four Scandlines ferries run to Rødby on the Danish island of Lolland every half hour, around the clock, over the eighteen kilometres of the Fehmarn Belt. Both are living on borrowed time. The Fehmarn Belt Tunnel, under construction since January 2021, is a 17.6-kilometre immersed tube assembled from seventy-nine concrete elements of 217 metres each — when it opens it will be the longest immersed tunnel in the world, and it will turn a forty-five-minute ferry crossing into seven minutes by train. A second tunnel is being built under Fehmarn Sound. The island that spent a thousand years as a place you reached by boat is about to become a place most travellers pass beneath without stopping.