The Lencois Maranhenses lagoons at sunset, from Lagoa Bonita

Sunset is not an extra on a Lencois Maranhenses day; it is the way the day is built. The state tourism office says lagoon trips mostly head out in the afternoon, once the sun has dropped a little, and that the Lagoa Azul outing closes with everyone up on the dunes for sunset.^5,6 The midday glare on white sand is fierce, so the best hours belong to the late afternoon.

Seeing the Lencois Maranhenses lagoons at sunset is also a matter of geometry. The dunes are white quartz, the lagoons are shallow and clear, and as the sun drops the sand turns from blinding white to cream, gold and pink while the water goes from turquoise to deep blue. NASA's explanation of the colours, light reflected off the sand through shallow water, is easy to watch changing in real time.⁷

The tour sold on this site is designed around that moment. It spends the first part of the day around Lagoa Azul and the later part around Lagoa Bonita, breaks for a meal at a local restaurant in between, and saves the sunset at Lagoa Bonita for last. Your guide times the climb so that the group is on the crest well before the sun goes down.

Barreirinhas sits just south of the Equator, so the sun rises and sets at much the same time all year, and the length of daylight barely changes between the months. That steadiness makes planning easy: the sunset comes at much the same hour whatever month you travel, and your tour will be timed to reach the top of the dunes in good time before it. Expect the sky to darken quickly once the sun has gone, as it does everywhere in the tropics.

What changes through the year is not the clock but the scene. From May, the park plan describes full lagoons and settled weather, the best combination for a sunset with water in it.¹² The state's wet season runs from January to July, months when cloud can hide the sun but also set the whole sky alight.¹³ After that the water drains away little by little, and by December, NASA notes, most lagoons have gone.¹⁴ In the dry months the lagoons shrink, and the state tourism office notes that the sand often takes on golden and pink tones as it reflects the sunset.³

If the sunset is your priority, think about crowds as well as weather. July is the busiest month in the park, and the Lagoa Azul and Lagoa Bonita area draws more visitors and vehicles than anywhere else in it.^12,15 In those weeks the main crest gets busy, so a guide who walks you a few minutes further along the ridge is worth more than a perfect forecast. Weekdays outside the July holidays are calmer still.

After the sun goes down, the light fades fast. You walk back over the dunes and down to the vehicles in twilight, then ride back toward Barreirinhas in the dark. The tracks are sandy, bumpy and unlit, and only accredited vehicles and drivers are allowed to carry visitors in the park.⁹ Sit back, hold on, and let the driver do the work; the stars often come out before you reach the road.

Prepare for that last hour before you leave in the morning. A headlamp or phone torch helps on the walk back, a light long-sleeved layer keeps off the evening breeze and the insects, and ICMBio's advice to carry insect repellent matters most at dusk.¹⁶ Keep your water bottle handy too: you will have spent the hottest hours of the day on the sand, and dehydration catches up with people at the end of the day.

Pickup at your lodging is part of the combo day; confirm at booking where the vehicle drops you after dark. If you are on a half-day sunset trip instead, check where it ends before booking, and whether it collects you from your lodging. The half-day Lagoa Bonita trip, for example, runs 5 hours, including a ferry across the Preguicas river and an off-road vehicle over sandy tracks.

When the last light goes, the sky takes over. ICMBio's public use plan notes that the park offers one of the best opportunities for night-sky observation in Brazil, and lists stargazing among the activities on offer.^4,24 With little artificial light across the dune field, the Milky Way can be bright on moonless nights. Give your eyes time to adjust away from torches and screens.

A Lencois Maranhenses night tour usually means one of two things. One is a night in the oasis villages on the crossing, where the dark is complete.²⁵ The other is a short evening trip from Barreirinhas: one listing runs a 3-hour stargazing tour by speedboat on the Preguicas river, with binoculars and astronomical instruments, from $53. Ask if that figure is per head or for your whole party before you book.

Plan the night around the moon. A full moon lights up the white sand almost like day, which is magical for a walk but washes out the stars. A new moon gives the darkest sky. Remember that the park bans fires everywhere, so there are no bonfires on the dunes, and walking out alone at night is a bad idea in a place where it is easy to get lost.^17,18 Stargaze with a guide, or from the edge of town.