Nature

Geology of the Basque Country: flysch, caves, gorges and desert

Basque Country landscapes explained: Zumaia’s flysch cliffs, the caves of Sare, Isturitz, Ekain and La Verna, the Kakuetta and Holzarté gorges, Bardenas Reales.

By Eztebe4 min

The landscapes of the Basque Country tell a story tens of millions of years long: seabeds turned into cliffs, rivers that have carved through limestone, caves where people lived and painted. Here are the places where you can read it in the open air… and underground.

Flysch: the pages of a stone book

The Basque Coast Geopark

Between Mutriku, Deba and Zumaia, the Basque Coast Geopark covers 89 km². Recognised by UNESCO, it is part of the Global Geoparks Network. It protects karst landscapes and, above all, the famous flysch cliffs.

What is flysch?

Flysch is an alternation of layers of marine sedimentary rock, stacked like the pages of a book. At Zumaia, these layers record continuous sedimentation over a very long period, from the Cretaceous to the Eocene.

The Cretaceous–Paleogene boundary

From Itzurun beach you can see the Cretaceous–Paleogene boundary, the trace of the extinction that happened 66 million years ago and marked the end of the non-avian dinosaurs. In 2022, the Zumaia stratigraphic section was selected by the International Union of Geological Sciences as one of 100 world geological heritage sites.

Tip: check the tides and take care at the foot of the cliffs.

Underground: caves and chasms

The Verna chamber (Sainte-Engrâce)

In the Pierre-Saint-Martin cave system, discovered in 1953 and holder of several world caving records, the Verna chamber (salle de la Verna) measures 255 × 245 × 194 m. Its operators bill it as the largest lit underground chamber in the world. Opened to the public in 2010, it can be visited all year round, by reservation only (no children under 5), with options ranging from a discovery tour, accessible to wheelchair users, to a descent to the underground river. See Sainte-Engrâce (Santa Grazi).

The Sare caves

Occupied by humans for at least 45,000 years, the Sare caves can be visited on a sound-and-light tour, at 14°C all year round. Thirteen species of bats live there, protected since 1999. Booking essential. See Sare (Sara).

The Isturitz and Oxocelhaya caves

At Saint-Martin-d’Arberoue, inside Gaztelu hill, are two caves one above the other: Isturitz, an archaeological site with cave engravings, and Oxocelhaya, 15 m below, with spectacular rock formations. About 600 m of passages and 80,000 years of human presence. Guided tours from 15 March to 15 November.

Ekain, prehistoric horses

Ekain cave (Zestoa), discovered in 1969 and made a UNESCO World Heritage Site in 2008, contains painted horses considered among the most perfect in Palaeolithic art. The original cave is closed; its replica, Ekainberri, can be visited 600 m away.

Santimamiñe

In the Urdaibai reserve, near Guernica (Gernika-Lumo), Santimamiñe cave bears witness to human presence since prehistoric times.

Gorges: water against rock

The Kakuetta gorges

At Sainte-Engrâce, the Kakuetta gorges stretch for just under 4 km, with walls 30–350 m high; at the ‘Grand Étroit’ (the Great Narrows), only a few metres separate the two cliff faces. The visitor trail used to end at a waterfall of about twenty metres.

The Holzarté gorges

At Larrau (Larraine), the Holzarté footbridge spans the Olhadubi canyon at a height of more than 150 m. See the best hikes.

Limestone and water: karst

  • The source of the Urederra (Navarre): a nature reserve in the Urbasa-Andía park, accessible by reservation only.
  • The Purón gorge (Valderejo, Álava): a canyon carved by the river through the limestone, a fine example of the karstic action of water.
  • The Arditurri mines (Aiako Harria): worked from Roman times until 1984, they yielded silver, iron, lead, zinc and fluorite.

A desert in Navarre: the Bardenas Reales

In the south of Navarre, the Bardenas Reales (41,845 hectares) offer a unique semi-desert landscape: formations sculpted by erosion, such as the famous Castildetierra, gullies and plateaus. The area has been a UNESCO Biosphere Reserve since 7 November 2000. See Tudela.

Further reading

Sources

Ongi etorri — happy exploring!

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