The best option to get to Lencois National Park is to reach the capital of Maranhão first. From there, you can book tours or take public transportation to the town of Barreirinhas which is located just outside the national park.
Cavernas do Peruaçu National Park
To get to Cavernas do Peruaçu National Park you should rent a car at the closest airport in Montes Claros.