Eco Travel (Av. Jaguararí 4990, Green Mall, Loja 26, Candelária, tel. 84/3234-4068, www.ecotravel.com.br ) offers a variety of Jeep tours and expeditions up and down the coast as far as Jericoacoara  in Ceará . Trips can be customized for groups as small as two people and include various forms of accommodation as well as bilingual guides.
Cariri Ecotours (Av. Prudente de Morais 4262, Loja 3-B, Tirol, tel. 84/3234-4068, www.caririecotours.com.br ) has a really interesting assortment of guided tours by Jeep, van, and small buses throughout Rio Grande do Norte and the neighboring states of Ceará, Paraíba, and Piauí (including many into the Sertão) that mix natural and cultural attractions. Lasting from one day to one week, trips are customized for small groups and are led by multilingual guides.
Aside from many buggy excursions up and down the coast, Buggy & Cia. (Rua Guilherme Tinoco 1274, Tirol, tel. 84/9416-2222, www.buggyecia.com.br ) offers a fantastic 12-day adventure to the Parque Nacional dos Lençóis Maranhenses , which combines hiking with transportation by truck and boat.