The name is Tupi and it means the den or lair of the sea turtles — jericoacoara, worn smooth by five centuries of Portuguese pronunciation into the shorthand everyone now uses, Jeri. The word covers three different things that visitors regularly confuse. There is the beach. There is the village, a district of the municipality of Jijoca de Jericoacoara. And there is the national park, created around both of them, spilling across the boundaries of three municipalities — Jijoca de Jericoacoara, Cruz and Camocim — on Ceará's western coast, roughly 300 kilometres from Fortaleza. Until 1985 there was really only the first two: a beach and a settlement of fishermen, effectively cut off from the rest of the country by the same sand that now draws people to it.

Protection came in layers, and each layer was a response to the last one failing. An Environmental Protection Area was established on 29 October 1984 by federal decree, covering 8,416 hectares and including the village inside its boundary. That framework proved too permissive for what was coming. On 4 February 2002 the Jericoacoara National Park was created, superseding the protection area with a far stricter regime, and a separate protection area was drawn around the village's outskirts specifically to stop the settlement expanding into the fragile dune systems around it. In September 2005 that 207-hectare buffer was absorbed into the park itself. A further boundary revision in June 2007 pushed the park's edge one kilometre out to sea. The park today covers 8,862.89 hectares — about 88.6 square kilometres — and is managed by ICMBio, Brazil's federal conservation institute, under IUCN Category II.

Pedra Furada is the icon: a sea-worn rock arch standing at the tide line, and the formation everyone agrees is the emblem of the place. It also does something specific. Between 15 July and 15 August the setting sun lines up with the opening and drops through the arch, and for one month a year the rock becomes an instrument for watching the sky. The other daily ritual happens a few kilometres away at the Duna do Pôr do Sol, near Praia das Canoas — a dune high enough that the whole village climbs it in the late afternoon to watch the sun go into the Atlantic. Inland, the dune field is punctuated by freshwater lagoons: the Lagoa do Paraíso and the Lagoa Azul, whose transparent shallows and encircling sand have earned the region the nickname Caribe Nordestino, the Caribbean of the northeast.

The trade winds that scour this coast are the engine behind everything. They build and move the dunes, they keep the water surface broken and the air cooler than the latitude suggests, and they have made Jericoacoara one of the most heavily used windsurfing sites in the country. Sandboarding works on the same raw material from the other direction. The wind is also why the shape of the landscape is provisional: dunes here migrate, burying and uncovering things on a timescale of years rather than centuries, which is precisely what makes drawing a permanent boundary around them so awkward a piece of policy.

Behind the beach, the park protects a genuinely complicated set of habitats — mobile dunes, fixed dunes, freshwater lagoons, mangrove and coastal scrub — stacked against each other within a few kilometres. Surveys have recorded birds from 38 families here, including species that are rare or formally threatened, and the lagoons and coastal waters support fish, cetaceans and small to medium-sized mammals. The tension the park exists to manage is straightforward and unresolved. In 1994 the Washington Post named this one of the ten most beautiful beaches on the planet; in 2014 the Huffington Post ranked it fourth best on Earth. Every one of those endorsements brings more people to a dune system whose defining characteristic is that it cannot hold still and cannot be repaired.