Two areas are clearly obvious from the geological point of view and taking into account the landscape: the steep, rocky limestone ridges, with grazing areas in some of the valleys such as Urbia; and a series of siliceous hillocks and passes covered with vegetation only allowing small areas of rock to peep through here and there.
The former comprises the high ridges of Aloña-Aitzkorri-Aratz, an extremely important landmark on the landscapes of both Gipuzkoa and Alava. To see it for yourself, simply head for the Valley of Oñati for example, or drive along the N-1 road via Idiazabal-Etxegarate and the Alava Plain. The latter forms the long, gentle crest of Urkilla-Elgea, which can be seen in its entirety from all the roads on the plain. The first wind park in the Basque Autonomous Community was constructed on its hilltops.
From Arantzazu (Oñati), located on the gully of the same name and home to a magnificent sanctuary, several mountain paths will lead us to the meadows of Urbia (including a shelter and hermitage), situated at the foot of the highest part of the range. From Araia we can climb to the top of Aratz (1,443 m) and there, walk on varied tracks. In Aretxabaleta and Eskoriatza, we will find ourselves at the foot of Elorreta (Kurtzebarri, 1,146 m), an outstanding limestone crag on the far western stretch (Zaraia Mountain Range).
Three of the rivers in Gipuzkoa: Deba, Urola and Oria, have their sources on the foothills of this mountain range. On Alava's side, the waters flow into the upper course of the River Zadorra -and its reservoir- and the River Arakil-, which flows towards Navarre.
Karstic phenomena are as remarkable here as they are on all of our limestone mountains: fields of lapies, circular depressions, dolinas and multitude of caves, some of which are frequently visited, like that of Leze in Eguino. Many caves such as Arrikrutz and Aizkirri are prehistoric and paleontological sites that accommodate remains of cave bears and lions. The mountain range is also part of the Way of Saint James.
From the Otzaurte Pass, we will get to the San Adrián Tunnel, a natural cave that historically has been an access road between Gipuzkoa and Alava. Besides, the area is dotted with a large number of open-air sites, dolmens, tumuli and monoliths, as well as it offers an interesting historical-arquitectural heritage represented by many hermitages, farmhouses, etc., being the most outstanding elements the Nuestra Señora de Arantzazu Sanctuary and the town of Oñati.
Organised activities: hill-walking, rock climbing, biking, guided tours through medieval Old Towns of neighbouring towns, as well as potholing in caves, bungee jumping, paragliding, canyoning, abseiling (although the former ones take place in the park area belonging to Alava).
Camping is allowed at nights, including bivouacing in outfitted areas. If you want to extend your camp time, you have to ask for permission.