From Navafría mountain pass (1773 m), in the village of Lozoya (Madrid), to Nevero Peak (2209 m) there is a route of about 7.5 km. round trip which apparently doesn’t involve much difficulty but with snow, wind, and fog can become a risky experience. I did the route this morning with my hiking group to finish the year.
Further information: Sierra de Guadarrama
A Crime is Afoot 