If there were a legendary cave in Portugal this one would certainly have this status, even though its speleological importance is reduced. Here, as in other natural holes in this region, tradition says that someone have put a dog or a cat inside a basket and thrown it into the cavity; a few days later the animal appeared floating in Alviela Spring. This unusual tracing technique was used because was heard the sound of running water coming from within.

Aderneira aven opens in limestones from the Middle Jurassic, at approximate 285 meters high. Despite its wide entrance, the progression does not exceed 40 m depth, due to a huge cone of blocks. Having accepted that the waters running in its interior were related to Alviela Spring, an iron railing was installed in the first third of 20^th century, to prevent the dumping of dead cattle into the aven interior, a very common practice in the humanized karst regions that has persisted in Portugal until recently. Studies carried out at the beginning of this century show this cavity was an element of an old groundwater circulation.