Nowadays many hikers cross the tunnel in order to gain access to the nearby peaks, forests and grazing fields, namely Aratz, Aizkorri and Urbia.

The status increasingly gained at that time by the San Adrian pass and the way coming south from Gascony down into Gipuzkoa was to have an important impact on the social, economic and constructing development of the population nuclei located on it and around.

The mountain pass was used for ages by shepherds, as evidenced by prehistoric traces of seasonal cattle migration, dolmens and burial mounds (usually small) in the area.

Place-names associated to alien cultures, such as neighbouring town Zegama or Arakama (commonplace family name in this region), claimed by some scholars to stem from Indo-European,[9] suggest that European peoples may have used this pass.

At any rate, this stretch is not located on the important axis Bordeaux-Astorga cutting its way east to west through the Alava plains (merging point with the Tunnel Route in Salvatierra/Agurain).

[11] After snatching the territories of Alava and Gipuzkoa from Navarre, Alfonso X encouraged the use of this stretch that connected by land Castile to Gascony through the strip extending from San Sebastian to Irun.

With a view to strengthening both trade and military grip in the region, the king founded in 1256 the towns of Salvatierra (Agurain), Segura and Villafranca (Ordizia) in various spots of the way,[12] so becoming popular with pilgrims, that could find there shelter and safety.

At the time, highwaymen frequenting the area are dreaded by pilgrims and travellers alike, who were not acquainted with the wild surroundings where local bandits could easily stalk and find a hideout.

"The San Adrian pass is good only for people on horse or on foot, since the carriage way exiting Vitoria goes through Salinas, Mondragon, Oñate and Villareal [from Gipuzkoa]", explains the arguably French Basque traveller J.C. Santoyo in 1612.

However, this stretch continues to be widely used up to the late 18th century, when the new King's Highway from Madrid to France is built in 1765 and traffic shifts, so spurring the definite decay of the San Adrian tunnel way.