If Sierra de Guadarrama mountain range would have a hearth you could see in the map a MTB beating in Cercedilla
You have to get up early to ride in Cercedilla. Any weekend before 10am there's almost no place to park your car. Streets are narrow in the old village and there's heavy flow of biker seeking for trails. Cercedilla hosts the Big Ride, one of the most important MTB Enduro events of the Spanish calendar and probably the only one with chances to bring the Enduro World Series to Spain.
Right after downloading the bike from the van a web of trails comes to mind, there are many options to climb, but of course not all available for everybody... you must have the power and the technic to climb them. In Cercedilla you have to earn your descent, fun starts after climbing almost 900 vertical meters. We climbed the antique Roman road and then the Republic's road, the easiest and "fastest" way up to La Fuenfria pass, The crossroads of all options. From this mountain pass that is part of the Way of Saint James there are choices for everybody.
We chose a special descent. We haven't discovered anything, but our guide Jorge has been years going all over Sierra de Guadarrama and collecting trails for himself, from this research he has created itineraries that link the most important landmarks of Madrid's mountains while riding the most funny, technical and flowy trails. As we said... we didn't go down the same way we came up. For more than one and a half hour we "flowed" down steep trails plenty of rocks where only the masters are able descend without stepping aside of the bike. If your riding skills and your mind let you, you'll start taking pressure off your brake lever and letting fun come in the shape of speed and smiles.
We enjoyed 4 hours, it could have been 8... and so by days without repeating rounds. As we reached Cercedilla again we sat in a terrace and had a couple of well deserved beers and chorizo tapas, we had earned it...