In 1944, with the country still under German occupation, the schoolteacher and conservationist Jac. P. Thijsse wrote about a stretch of dunes between Bloemendaal and the North Sea Canal that deserved protecting. Thijsse had spent decades fighting for Dutch nature - he founded Thijsse's Hof, a wildlife garden in Bloemendaal that opened in 1925 and is still the oldest in the country. His essay set something in motion. In 1950, De Kennemerduinen was established as a national park. In 1995, the park was expanded and renamed Zuid-Kennemerland, absorbing reserves managed by Natuurmonumenten and a constellation of private and public landholders. At 38 square kilometers, it is small by international standards. But it borders the Amsterdamse Waterleidingduinen to the south, and together the two reserves form one continuous dune ecosystem - the largest in the Netherlands.

Dunes in this part of Holland are calcium-rich, and lime in the sand allows plants to grow here that grow nowhere else in the country - delicate orchids in the slacks, dense thickets of bacciferous shrubs whose berries draw songbirds by the thousand. Over a hundred bird species have been recorded in the park, along with nearly twenty species of butterfly. Fallow and roe deer move through the inland woods. Foxes patrol the edges. In 2007 the park took a leap that surprised even its own staff: it released a small herd of wisents, the European bison, into a fenced section closed to visitors. Bison were last native here in the medieval period. From a purpose-built viewing platform - open only outside the spring birthing season - you can watch shaggy black-brown bodies move through grass that has not been grazed by something so large in eight centuries. Park managers are now openly talking about wolves and lynx, and watching the golden jackal creep north.

On the eastern edge of the park lies a strip of pine and oak forest called the Bloemendaalse Bos. During the German occupation it was a Wehrmacht shooting range. Resistance members captured by the Sicherheitsdienst were brought here to be executed. The most famous of them was Jannetje Johanna Schaft, known as Hannie - a law student from Haarlem who had cut her studies short when she refused to sign a declaration of loyalty to the occupier. She joined the resistance and attacked German soldiers and Dutch collaborators in the streets of Haarlem and Amsterdam. The Nazis called her 'het meisje met het rode haar' - the girl with the red hair. She was arrested at a checkpoint in March 1945. On 17 April 1945, in these dunes, two SS officers brought her out to die. The story they tell in Haarlem is that the first shot wounded her and she said, 'I shoot better than you.' She was 24. The Netherlands was liberated 18 days later. A memorial stands in the woods now, and every year on the first Sunday after her death, people come and lay flowers.

Today the park gets 1.8 million visitors a year. In summer, a small fresh-water pond on the road between Bloemendaal and Zandvoort - locals call it 'het Wed' - fills with families on towels and children with inflatable rings. The train from Amsterdam to Zandvoort beach runs straight through the dunes; on a Saturday in July the carriages are jammed with surfboards and bicycles. There are estates inside the park where Amsterdam merchants once built summer houses. There are abandoned water-extraction works from when the dunes still supplied Haarlem's drinking water - a practice that ended in 2003 to let the groundwater rise again. And there are the woods at the eastern edge, where the path narrows and the trees close in, and the wind carries something that does not feel quite like wind.