The route leaves the village of Navacerrada and climbs to the Puerto de Navacerrada, on the border between Madrid and Segovia. From there it follows the ridge of the range to the Puerto de Cotos and then, on the M-604, drops down towards the Lozoya valley as far as Rascafría. It is two passes back to back and a long descent, a short ride that is easy to extend with other passes in the area.
The whole route runs through the heart of the Sierra de Guadarrama, around the national park, and crosses the municipalities of Navacerrada, Los Baldíos, the Real Sitio de San Ildefonso and Rascafría. On the climb you leave behind the view over the Madrid plain; at the top the scenery is pine forest and high mountain, and the descent to the Lozoya is a run of linked bends through the pines with the valley opening up ahead. Near Rascafría stands the Monasterio de El Paular, a good stop at the end.
It is about 33 km and a little over 50 minutes without stops, with around 90 bends and no tight hairpins. Altitude ranges from about 1,140 m to 1,861 m at the top, so it is much colder up there than in Madrid. At weekends there is heavy traffic, full car parks at the passes and many cyclists going up and down: overtake only with clear visibility and take the descent at a steady pace.