The Lizarrate or Túnel de San Adrián is a natural cave and historical passage located in the Aizkorri-Aratz Natural Park, between the provinces of Araba and Gipuzkoa. This unique geological formation has served as a key transit point for centuries, linking the interior of the Basque Country with the province of Gipuzkoa and the northern trade routes.

Since ancient times, the tunnel has been a strategic passage through the Basque mountains. Archaeological evidence suggests that it was used as a transit route during prehistoric times. During the Roman period, it formed part of an important road connecting the Ebro Valley with the Bay of Biscay. In the Middle Ages, it became a vital communication route, used by traders, shepherds, and military forces. The natural tunnel, approximately 50 meters long, provided a sheltered crossing in an otherwise rugged and challenging terrain.

One of the most notable aspects of the Túnel de San Adrián is its connection to the Camino de Santiago. Pilgrims following the Camino Vasco del Interior passed through this tunnel on their way to Santiago de Compostela. This route, an alternative to the coastal and French ways, was frequently used in medieval times, as it provided a direct path from France into Castile. The tunnel’s strategic location made it a well-known landmark among travelers.

At the entrance of the tunnel stands the Chapel of San Adrián, a small chapel dedicated to Saint Adrian, which gave the site its name. Historically, it served as a place of rest and protection for travelers. Nearby, remains of an ancient watchtower and fortifications are visible, indicating the site’s historical role in controlling movement across the mountains.