Moving inland from the coast, we discover the world of karst; a spectacular landscape created by the erosion of limestone, formed in the distant past under a tropical sea. The chalky composition of the stone and the effect of water upon it for millions of years, explain the existence and proliferation of numerous caves, chasms, channels, sinkholes, underground rivers, ravines and rocks of capricious forms.
Humans have occupied the Deba valley for about 200,000 years. Deba has more than fifty caves and prehistoric sites that constitute one of the most important groupings from the Paleolithic period on the entire Cantabrian coast. The important archaeological remains found in this environment confirm the presence of two types of humans: Neanderthals and Cro-Magnons. It is not a coincidence that many have denominated the area "the little Dordogne".
Almost all of the inland area of the municipallity of Deba is within the geographical area of the Izarraitz massif, an area proposed as a "Site of Community Importance" (SCI). It is in this area where Itziar, the Lastur valley, as well as the small rural nucleus of San Nicolas de Lastur are found.
Only 6 km from the urban center of Deba, at the foot of the karst massif of Andutz, is Itziar, an important center of devotion to Mary, where the sanctuary of the same name is located. The temple is presided over by the Romanesque image of the Virgin of Itziar (12th century), one of the most beautiful of Basque iconography, inspiring great devotion among these seafaring people.
Next to the Itziar sanctuary is the sculpture Amatasuna (Maternity) by Jorge Oteiza. Developed as a tribute to his wife Itziar, it represents the concept of motherhood in the broadest sense of the word. Contemplating it from different angles, it offers three different visions, three transcendental moments of motherhood. It is an existential gap that, just as a mother would, protects all visible surroundings, Amalur (Mother Earth).
Itziar is an ideal starting point for excursions into the surrounding areas. From here, we can walk to the neighboring areas of Endoia, Mardari, Arbiskoa or Lastur, and climb to the summits of Andutz (613 m.), Otarre (663 m.), Agiro (739 m.), Sesiarte (758 m.) and Erlo (1030 m.), authentic panoramic viewpoints of spectacular Basque geography.
Continuing inland, we will enter the Lastur Valley, a paradisiacal place worth visiting to discover it slowly, on foot and without haste.
At the end of the valley is the tiny rural nucleus of San Nicolás de Lastur, which has a shrine of the same name, the Plazaola mills (former ironworks), a fronton, just four and the hostel, where we can visit the karst interpretative space and get to know through information panels, photographs and illustrations, the history and traditions of this valley, its link with stone and its geological characteristics, as well as the ways of life and customs of its inhabitants. A valley where the farmhouse, the caves, the water, the limestone and the bulls are the main protagonists.
The Lastur valley appears already mentioned in a document of 1335, in which King Alfonso XI, at the request from the foundries of the valley, authorised trees to be cut in the nearby communal mountains. As time goes by, the foundries of the valley became mills and witnesses to this are the Plazaola mills, which can be visited in a perfect state of conservation and operation.
From the same square, next to the shrine begins the path PR-46 or the Karst Route. A route of great scenic and geological value through the heart of the Geopark.