Parque Natural de Aiako Harria
Rising dramatically just south of Irún, the Parque Natural de Aiako Harria (known in Spanish as Peñas de Aia) is a UNESCO-recognised biosphere reserve of ancient oak forest, granite massifs and rushing streams that feels a world away from the border town below. The three summits — Txurrumurru, Erroilbide and Irumugarrieta — are all accessible as day hikes from Irún.
Best trails from Irún
The most popular route starts at the Artikutza road trailhead near the Oianleku area and climbs through Atlantic oak woodland to the Irumugarrieta ridge (1,016 m), rewarding hikers with views spanning the Bay of Biscay, the Pyrenees and on clear days the distant outline of the Cantabrian mountains.
A shorter and family-friendly option follows the Añarbe reservoir trail through beech and oak forest to a series of small waterfalls — flat enough for children, beautiful enough for serious photographers.
Wildlife and seasonal highlights
The park is home to Pyrenean desman, otters along the Añarbe river, and a rich population of woodland birds including black woodpecker and honey buzzard. Autumn turns the forest copper and amber in a display that rivals anything in the Pyrenees proper.
Spring brings carpets of wood anemone and wild garlic under the oaks; summer is ideal for summit walks when the granite boulders are warm and dry. Winter can bring snow above 700 m — crampons are advisable for the upper ridges from December to March.
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