The route leaves Torrelaguna, passes Patones and continues on the M-102 and M-133 towards the El Atazar dam, which the road goes past. It then carries on to the village of El Atazar and, on the M-131 and M-127, skirts the reservoir to Cervera de Buitrago. It also uses stretches of the M-134 and M-914.
It crosses the municipalities of Torrelaguna, Patones, Uceda, El Atazar, El Berrueco, Puentes Viejas, Robledillo de la Jara and Cervera de Buitrago, in the heart of the Sierra Norte. The landscape is scrub, slate and ravines, with the El Atazar reservoir appearing and disappearing between bends. Patones de Arriba, with its slate houses, is worth a stop at the start.
It is about 57 km and almost two hours without stops: a slow road, with more than 150 bends and one hairpin. Altitude ranges from about 690 m to just over 1,090 m. The road is narrow in many places, with blind bends and possible gravel or fallen stones. There may be loose livestock. Check beforehand whether the road past the dam is open.