The route leaves Rascafría and runs along the Lozoya valley on the M-604, passing Pinilla del Valle beside the Pinilla reservoir. Near Lozoya it climbs on the M-637 to the Puerto de Navafría and, on the other side, drops on the SG-612 to the village of Navafría, in Segovia province. It also includes a stretch of the M-973.
It crosses the municipalities of Rascafría, Pinilla del Valle, Lozoya, Aldealengua de Pedraza and Navafría. The first part is a broad, quiet valley, with the reservoir and mountains on either side; then the road heads into the pine forest and the bends link together on the way up and down. The Segovia side is dense forest until you come out at the village.
It is about 34 km and a little over an hour without stops, with more than 90 bends and seven hairpins. Altitude ranges from about 1,100 m to 1,781 m. It has less traffic than Navacerrada, but in the forest there can be damp shaded patches, and livestock near the road in the valley. Keep to a pace at which you can stop within the distance you can see.