Aiako Harria Natural Park

Aiako Harria Natural Park covers 6,913 hectares at the eastern tip of Gipuzkoa, between the rivers Bidasoa and Urumea. It contains the only Palaeozoic granite outcrop along the entire Basque Cantabrian coast, a geological distinction that sets it apart from any other protected area in the region. Three main peaks—Irumugarrieta (834 m), Txurrumurru (821 m) and Erroibide (837 m)—rise as dark granite masses above a dense mantle of Atlantic forest. From a distance, their jagged profile is unmistakable against the grey-green Cantabrian sky.

Annual rainfall exceeds 2,200 mm in the lower areas and can reach 2,800 mm on the summits, making Aiako Harria one of the wettest spots in the Basque Country. That persistent rain feeds a network of streams and brooks flowing from the peaks towards the Oiartzun and Urumea rivers, sustaining pedunculate oak woodland, acidophilic beech forest and alder-lined riparian corridors in good condition. Beneath the canopy, ferns and mosses carpet the ground in an unbroken green layer punctuated only by lichen-covered granite blocks. The smell of damp earth and decomposing leaf litter accompanies every walk through the forest interior.

The fauna is Eurosiberian in character, with over 147 recorded vertebrate species. Roe deer and wild boar are the most frequent mammals, while the European mink—one of Europe's most endangered species—and Atlantic salmon inhabit the park's watercourses, giving these rivers first-order conservation value. Notable birds include griffon vulture, peregrine falcon nesting on the granite cliffs, and middle spotted woodpecker, an indicator of mature forest with old-growth trees. Streams descending from the peaks support native brown trout and white-clawed crayfish populations.

The territory is shared among five municipalities: Oiartzun (44.7%), Errenteria (25.1%), Irun (18.2%), Hernani (9%) and Donostia-San Sebastián (3%). The Arditurri mines, worked since Roman times for silver, lead and fluorite, are now open to visitors along more than 800 metres of lit galleries with interpretive panels covering 2,000 years of extraction. Nineteenth-century mining infrastructure blends into the woodland landscape, creating a contrast between industrial heritage and natural recovery.

From the three summits on clear days, the Cantabrian coast is visible to the north—including Txingudi Bay and the Bidasoa estuary—while the first Pyrenean foothills appear to the south. The trail network includes circular routes of varying difficulty: easy valley-floor walks for families, moderate ascents to intermediate viewpoints, and ridge traverses for experienced hill-walkers. The park was declared in 1995 by the Basque Government (Decree 241/1995), protecting this singular granite enclave and its associated Atlantic forests.

Proximity to San Sebastián—just 20 kilometres from the city centre—makes it possible to combine a morning in the mountains with the gastronomic and cultural offer of the Gipuzkoan capital. Oiartzun, the municipality with the largest share of parkland, has traditional cider houses where the cider season (January–April) draws visitors from across the province. The closeness of the French border also links Aiako Harria to the French Basque Country, enabling cross-border excursions through shared landscape.