The visit to this place must be done with great, great caution.

One of the iconic caves in Portugal mainland. Its name comes from the fact that several caves opens in the magnificent Chainça karren field and because some have served as shelter for red-billed chough (Pyrrhocorax pyrrhocorax chough in Portuguese is gralha), a bird once very common in this region. This was the 7^th, of many, to be identified in this small heap that rises near the southern limit of Sto. António Plateau. Its modest entrance in limestone of the Middle Jurassic, at an altitude close to 350 meters, does not reflect its great importance (geological, landscape, historical and speleological).

The access well has 70 meters deep, opening into the ceiling of a room at the intersection of several galleries. Part of its fame comes from the magnificent aspects of its underground landscape, with stalactites, stalagmites… - some with active runoff - punctuated by small temporary lakes due to precipitation. However its exceptional importance comes from the fact that few caves in this sector of the Estremenho Limestone Massif can intersect zones with traces of fossil or current circulation.

The vast Cabeço da Chainça karren field is a bare karst, with no soil, where the larger karren forms seem to be driven mainly by the action of dissolution processes on the diaclase system, combined with other smaller dimensions forms on its surface.

The vegetation, typical of these karstic environments, develops where there is soil accumulation. The depth of some crevices between lapiaz, sometimes with walls that seem to be carved by people, turn walking a dangerous activity. You need to jump from slab to slab, and this is difficult because vegetation is dominated by kermes oak (Quercus coccifera).

Aven, swallow-hole, shaft or natural well – from the Arab al-gar (hole). Natural well in limestone or volcanic terrain, resulting from the falling of caves’ ceilings or vaults as well as sinkholes.

Diaclase – fracture of a rock without movement.
Lapiaz or karren field - common landscape in limestone areas, with many grooves due to the dissolution of limestone by rainwater along fractures and cracks.