The discovery of the Altxerri cave and its prehistoric sanctuary was made in two very different phases.

The existence of caves in the area was unknown until in 1956 the road was being built which passed in front of the Altxerri farmhouse. A temporary quarry was excavated to extract construction material from the limestone behind the farmhouse.

One of the dynamite blasts blew open a hole one metre wide and 80 cm high, revealing a long wide gallery.

Shear of the old quarry whose exploitation led to the discovery of the Altxerri cave.
(Ω) shows the opening originated by the quarry