Lençóis Maranhenses National Park

Take off your shoes. The sand here is fine and pale, and it stays surprisingly cool under your feet. It feels almost like flour. Ahead of you, the dunes roll away in long white curves, one after another, as far as you can see. Between them, there is water. Clear pools of blue and green lie in the hollows, still and bright under the sky. Listen for a moment. Mostly you will hear the wind, and the soft hiss of sand moving across sand.

Welcome to Lençóis Maranhenses National Park, on the northern coast of Brazil, in the state of Maranhão. The name comes from Portuguese. Lençóis means bedsheets, and from the air the dunes look exactly like that — white linen spread out to dry, wrinkled and folded by the wind. You are standing at the edge of it from Santo Amaro do Maranhão, a small town that sits closer to the dunes than almost any other settlement around the park.

Here is the first surprise. This is not a desert, even though it looks like one. A true desert receives very little rain. This region receives a great deal of it, mostly in the first half of the year. That rain is the secret of the whole landscape. Without it, you would see only sand. With it, you see thousands of lagoons appear between the dunes, filling the hollows like glass dishes set out across the land.

So why does the water stay? Beneath the sand lies a harder layer that does not let the water drain away quickly. Rain collects on top of it, in the low places between the dunes. As the rainy season ends and the dry months begin, the lagoons slowly shrink. Many of them vanish completely. The next year, they return, though never in quite the same shape or the same place. You are looking at a map that redraws itself every year.

The sand itself has travelled a long way to reach you. Rivers carry sediment from deep inside the continent down to the Atlantic coast. The ocean pushes that sand back onto the beaches. Then the steady winds from the sea pick it up and drive it inland. Over a very long time, this movement built the dune field around you. The dunes are still moving now, slowly, grain by grain, shaped by the same wind that touches your face.

The government of Brazil protected this landscape as a national park in 1981. It covers an enormous area — well over one thousand square kilometres of dunes, lagoons, rivers, mangroves and coastline. In recent years, it was also added to the UNESCO World Heritage list, which recognises places of outstanding value to all humanity. For a place that changes shape every season, that kind of permanent recognition carries a quiet irony.

Now for the second surprise. Look closely into the lagoons, and you may see small fish. How can fish live in water that disappears every dry season? Scientists and locals both point to several possible answers. One fish often mentioned is a kind of wolf fish, which is said to bury itself in wet mud and wait for the rains. Other life may arrive with birds, or through connections to nearby rivers in the wettest months. The full story is still being studied.

People live here too, and that is easy to forget when you stand in all this open space. Small communities have lived around and even inside the dune field for generations. Some families fish, some keep goats or cattle, and some grow cassava, a starchy root that is a staple food across northern Brazil. Their villages sit in green pockets where water and soil allow plants to grow. Life here follows the rhythm of rain and drought, and of the moving sand.

The town of Santo Amaro gives you a different view from the busier gateway towns to the east. It is smaller and quieter. From here, the dunes begin very close to the houses, so you can feel the edge between town and sand quite sharply. Getting deeper into the park usually means a sturdy four-wheel-drive vehicle and a local driver. Some routes cross shallow rivers, and the tracks shift with the seasons, just like the dunes.

When you climb a dune, take your time. The slope that faces the wind is firmer and gentler. The other side is steeper and softer, where sand slides down in small avalanches. From the top, the view opens up. You see the pattern of the whole place — the white crests, the coloured water, the dark lines of distant vegetation. On a clear day, the light is so strong that the sand can hurt your eyes, so sunglasses help a great deal.

The colours of the lagoons change through the day. In the morning, the water often looks pale blue and calm. Around midday, with the sun high, it can turn a bright green or turquoise, and the sand glows almost white. Late in the afternoon, the shadows grow long. The dunes turn gold, then pink, then grey. Many visitors stay to watch the sunset from a high ridge, and the walk back across the cooling sand becomes part of the memory.

This is a fragile place, even though it feels endless. The dunes have no shade, no shops and few marked paths. Water is precious. Footprints disappear with the wind, but rubbish does not. Respect the guidance of local drivers and guides, who know where the sand is safe and where the lagoons are deep. And swim gently. These pools are fresh rainwater, warmed by the sun, and they are home to more life than you might expect.

Before you leave, stand still for one more moment. Look down at the sand around your feet. Each grain came from somewhere far away and will move on again soon. Look at the nearest lagoon and the line where water meets sand. Next season, that line will be somewhere else. As you walk back, notice your own footprints already softening behind you... This landscape keeps nothing for long. That is exactly what makes it worth seeing today.