The beginning of this route is very near of “hayedo de Montejo”, at the opposite side of the bridge over the river Jarama (province of Guadalajara). A hundred meters following the road from this point you will see a forest trail (closed normally to traffic of cars with a barrier) that enters into the oakwood and goes up by the valley of river Jarama (the river stay on the left of our way).
A few minutes afterwards you will arrive next to a meadow with livestock (there are cows and sheeps by these valleys) where there is a junction; take the forest trail of the right (Ermito valley) and follow until a nearby new junction; take again the right and continue by this trail, approaching to the West face of Santui (1.927 m.). The forest trail turn left, passing a stream. Climb to Loma del Ravinate, turning again on the right and then on the left. You will arrive to a meadow with a excellent view to Loma Mediana (W) and Tres Provincias (2.128 m.), named thus because this mountain is the only one where the provinces of Madrid, Guadalajara and Segovia meet.
From this point, the forest trail dissapear and a narrow path climbs straightly, crossing a pine-grove. Bushes replace pines and other trees when you reach the col of Calahorra (collado de la Calahorra, 1.849 m.) in the beggining of the slopes of the northern face of Santui. Here you can take a new forest trail (N) that ascends to the col of Agua Fría (collado del Agua Fría, 1.996 m.), two kilometers away. We are next to the last slope of El Cerrón, that appears like an undress summit, with a visible crest of rocks on the top.
Climb directly to this crest and follow to the summit (be careful in winter with the ice; the West face of El Cerrón is rugged). On the top there’s a pillar with a plate: It’s a bench mark (“vértice geodésico”). Exceptional view to Pico del Lobo (2.272 m.), Alto de las Mesas (2.257 m.) and El Cervunal (2.194 m.) to the north; Tres Provincias (2.128 m.) and Coto de Montejo (2.047 m.) to the west; Rocín (2.049 m.) and Ocejón (2.049 m.) to the east and Sierra del Rincón (Centenera, 1.810 m. and Tornera, 1.865 m.) to the south, in the border with the province of Madrid.