Gruta do Lapão is a major sandstone cave about 3 kilometres from the centre of Lençóis, accessible on a short trail through cerrado forest. The cave consists of several large chambers and tunnels — the main entrance hall is tall enough to walk through comfortably — carved into the red quartzite hillside by ancient rivers and flash floods. It stretches for over 600 metres and in some sections narrows to passages requiring ducking and scrambling.
Visiting requires a guide (available in Lençóis) and a headlamp or torch. The cave is inhabited by bats and contains some delicate rock formations; visitors are asked to stay on the established route. The combination of the unusual geology, the dramatic rock colours (the quartzite ranges from deep red to orange to pale pink), and the experience of moving through underground chambers lit only by torches makes Lapão one of the more memorable experiences near Lençóis.