Mostly about birdlife, shifting dunes and fresh water lakes, the latter in their best between May and September.
Motor vehicles are not allowed in the park, however, many agencies will offer 4X4 tours. These seem the best way visit the dunes - you have a guide who accompanies you.
The shifting dunes with the lakes in between are most spectacular at low sun, when a range of shadows come into play. Just after sunrise is probably the very best because of lower temperatures.
Flora and fauna
Dry sands don't cater for much. Some tiny fish in the lakes along with very small amounts of pond weed, the occasional bird and some bushes along the rim of the dunes.
Best time to visit is May - September, after the rains, and before the lakes dry out. The almost constant breeze may fool you into thinking the sun is not getting at you so be super careful and remember to constantly apply sun screen!
No such thing.
No motor transport inside the park, but plenty around the perimeter. No real roads though, so you need a good 4x4. Horses and donkeys are alternatives.
You may trek through the Lençóis - there are several different routes that vary in length and difficulty. Taking a guide is advisable but not needed for short treks, provided that you are an experienced hiker, well equipped and informed.
The environment will vary based on whether it's the dry or rain season. Best time to visit is between May and September when the lagoons are full of water. The advantage of this is that it is a nice sight, and you can use the water in the lagoons for drinking (after it is filtered or treated by tablets, boiled or etc.). This, however, may also present a disadvantage especially when trekking without a guide: you may need to trek around a lot of lagoons which would increase the length of your journey.
It is important to trek from east to west or east to south-west as that way you'll have the prevailing wind in your back. Otherwise you'd climb the dunes on their steeper side which has deeper sand. The opposing wind may also make the hike considerably harder and it will bring sand into your face. Do not wear contact lenses.
Fundamental equipment includes sunglasses, a hat that can be attached below your chin and plenty of water (3l per day is minimum - with this you'll probably need to use the ponds). If you trek without a guide, GPS, compass and a map are needed. Trekking poles are also useful. It is recommended to not wear boots but instead take sandals with socks or go barefoot (if your skin can handle the sun).
Trek across the dunes, swim in the many lakes and ponds, be dazzled by the beauty, listen to the silence of the area.
Most people sleep in Barreirinhas and do daytrips. However, the dunes are far more accessible if you stay in Atins, or even better in Canto de Atins. Mandacaru and Caburé are less convenient alternatives. Paulino Neves offers proximity to similar sights (Pequenos Lençóis), although not inside the actual national park. There is also the little explored town of Santo Amaro on the park´s western rim.
No restrictions so far, but there is some talking, due to garbage left behind. Do your part!
Brazilian authorities recommend that you get a yellow fever vaccine before travelling to this area.