The Aratz is a mountain of 1443 metres altitude belonging to the Basque Mountains. It is located between Guipúzcoa and Álava, Basque Country (Spain). It is the highest peak of the Sierra de Altzania, which is located to the east of the Aitzkorri massif.

Right on the dividing line between Alava and Guipuzcoa, the stones that mark the boundary between the two territories border the peak, and very close to Navarre, the Aratz is a large limestone mass that is visible and easily identifiable from a distance.

The 1443 metres of altitude of this mountain and the immensity of its size make it a reference point for the three territories that surround it. It is the highest in the Altzania mountain range and one of the highest in Álava (the fourth highest) and Guipúzcoa, and does not envy the neighbouring Aitxuri, the highest peak in the Basque Country.

One of its slopes rests on the historic San Adrián pass, which since ancient times has linked the Cantabrian slope with the Llanada Alavesa and the rest of the Iberian Peninsula. It has been a point of reference for walkers who have crossed these lands as it can be seen and distinguished from afar with its grey volcano shape.

The size of the mountain is immense, its summit wide. The summit is surrounded by a series of large hollows that usually keep the snow all year round. They are hollows 80 metres deep and not very wide, which have been used as snow pits.

To the north, the slopes of Aratz, covered in beech forest, overlook the Altzania valley in the lands of Guipúzcoa. To the south, it rises above the Asparrena valley in Alava, whose largest population centre is Araya, where oak and beech trees abound.

This area between the three territories is known as the Parzonería de Altzania, which has its origins in the exploitation of the richness of the forests and meadows by the surrounding villages.