Sierra de Aralar

The Sierra de Aralar extends between Gipuzkoa and Navarra as a gently shaped limestone massif reaching 1,431 metres at its highest point, the summit of Irumugarrieta. Its undulating plateau profile, dotted with dolines, limestone pavements and sinkholes amid upland pastures, is the product of intense karst weathering on Upper Cretaceous limestone over millions of years. Rainfall here exceeds 1,500 millimetres annually, seeping through rock fissures to feed an underground system of rivers and chambers that includes over 300 catalogued sinkholes—making Aralar one of the most speleologically dense massifs in the Iberian Peninsula.

Aralar's vegetation divides into two clear bands. Below 1,000 metres, Atlantic beech forests (Fagus sylvatica) drape the north and west slopes in a dark-green mantle that erupts into copper and gold in autumn. These damp, dense beech woods shelter an understorey of ferns, mosses and shade-loving plants where light filters as if through stained glass. When wind passes through the crowns, the forest produces a continuous murmur that accompanies walkers for hours. Above 1,000 metres, mountain pastures spread across wide campas where Latxa sheep—the native black-faced breed whose milk yields Idiazábal cheese—graze freely. On the campas of Enirio-Aralar, flocks range over hundreds of hectares of green meadow set against grey limestone outcrops.

Aralar's fauna blends Atlantic and montane elements. Griffon vultures maintain several breeding colonies on the massif's limestone cliffs, with groups of up to 40 pairs at some crags. Egyptian vultures arrive in spring from Africa to nest on the sunniest rock faces. Inside the beech forest, the white-backed woodpecker—a species tied to mature beech woods with abundant deadwood—finds in Aralar one of its southernmost strongholds. Mammals such as roe deer, wild boar, European wildcat and pine marten are regular, and European mink sightings in streams on the Navarrese slope place the sierra within the range of one of Europe's most endangered carnivores.

The Sanctuary of San Miguel de Aralar, perched at 1,200 metres on a natural vantage point, is the sierra's symbolic and devotional centre. It dates in origin to the 9th century and was enlarged in the 11th and 12th centuries with sober Romanesque limestone architecture. Inside, it preserves a 12th-century Limoges enamelled altarpiece, one of the most valuable pieces of medieval metalwork in the Basque Country. Every Whit Monday, thousands of pilgrims climb from the valley villages to the sanctuary in a pilgrimage that blends religious devotion with popular festivity. The farmsteads dotting Aralar's lower slopes sustain a pastoral economy that has shaped the landscape for centuries: dry-stone walls mark off meadows, bordas (shepherd's huts) are scattered across the summer campas, and small artisan dairies in nearby hamlets make Idiazábal from raw milk using methods passed down through generations.

Hiking routes criss-cross the sierra, ranging from two-hour walks to full-day traverses. The climb to the sanctuary from Baraibar (Navarra) via the Artubi pass is the classic option: 8 kilometres with 600 metres of elevation gain through beech forest and upland pastures. The full east-west Aralar traverse (28 km) links Zaldibia (Gipuzkoa) with Uharte-Arakil (Navarra) in a long stage that reveals the massif's landscape variety. In winter, snow blankets the high campas and the sierra lends itself to snowshoe routes, though frequent fog demands navigation experience.