This is the easiest route -as far as I know- to the summit of La Maliciosa, meaning only a 10 km hike to get there and back to the parking lot. An easy hike, for sure, available to most people with a basic physical training. All you have to do is walk uphill: a dirt road can take you from the Puerto de Navacerrada to the summit of the Bola del Mundo, and afterwards all you will have to do is stroll down to the Collado del Piornal and grab the summit of La Maliciosa. About two hours to get to the top (make it three and a half to four for the whole hike), a nice walk and (weather allowing) great views of the area around the mountain.
Puerto de Navacerrada
The trailhead for this route is the Puerto de Navacerrada, a mounatin pass placed northwest of Madrid and 1860 meters above sea level. There's a (not too big) ski resort up there, with skilifts based on the mountain pass and going up towards the slopes of Siete Picos
and Bola del Mundo. And, of course, a ski resort means buildings, bars, restaurants and so on. A good number of facilities allowing you to buy food or drinks but taking away most of the charm of the landscape.
Puerto de Navacerrada is 64 km away from Madrid, driving northwest. The best driving option is to take the A6 motorway for 43 km, up to exit 39 (signposted as “Villalba/Puerto de Navacerrada”). Leave the motorway and take road M-601 (grossly northwards) to Navacerrada (about 13 km to go) and Puerto de Navacerrada (an additional 7 km, making 20 km from the motorway).
Another option would be the M-607 highway to Colmenar Viejo, continuing afterwards to Cerceda and Navacerrada to enter there road M-601 to Puerto de Navacerrada. This second option offers a better landscape and might be helpful in case of heavy traffic congestion in the A6. If you are coming from the north, drive to Segovia and take road CL-601 towards La Granja and Puerto de Navacerrada.
When you reach the Puerto de Navacerrada, the biggest car park is placed east of the mountain pass(where the road to "Puerto de Cotos" starts)
The puerto de Navacerrada is also reached by an old mountain train departing from Cercedilla. If you choose this option, you would have to take a train to Cercedilla (line C-8b) at Atocha Railway Station (Madrid) and connect to the trains to Puerto de Navacerrada.
Buses to Cercedilla can be caught (lines 684 and 684A) at the Moncloa underground station (Madrid), allowing for connections with the Puerto de Navacerrada as they stop by the railway station when they reach Cercedilla. There are also buses to Puerto de Navacerrada (line 691) leaving from Moncloa.
The closest major airport stands at Madrid-Barajas.
Your starting reference is the lower station of the chairlift
leading east of the mountain pass. Look (it's easy) for that station and you will find by its side the beginning of a cement road leading uphill.
Follow it, it winds quite a lot around the mountain but if you follow that cement road it will take you to Alto de Dos Castillas
(2179 m, upper station of the chairlift) in 50 to 60 minutes. Should you prefer to walk uphill, cross-country, and avoid the dirt road, that's also possible. Just leave the road and climb the grassy (and bushy) slopes east of the Puerto de Navacerrada following the chairlift.
When you get to Alto de Dos Castillas you will have to follow the cement road eastwards to reach the summit of the Bola del Mundo
(2266 m, also known as Alto de las Guarramillas), easily identified by its huge TV antennas. Getting there will take 15 to 20 minutes.
It will be a first success for summit-baggers, and looking south from that spot you will be able to see La Maliciosa. Just follow one of several paths leading between the bushes towards the Collado del Piornal
and climb the final slope, remembering to follow the path and keep going slightly to your left (grossly south-southeast) until you reach the geodesical marking of La Maliciosa
The way back to Puerto de Navacerrada will be the same described in these lines, uphill to the Bola del Mundo and all the way down to the ski resort (either via cement road or direct downhill walking).
No special needs are required for summer climbs, just remember that good boots and walking poles do take care of your feet and knees. Whenever the weather prediction is doubtful or (of course!) in winter time take as good an equipment as you can get hold of. Good boots will be essential then, warm clothes, walking poles, food, drink, map and some kind of an orientation device (either GPS or compass). Guadarrama is a mountain area and you will be over 2200 meters high, you won't want to get caught by fog, rain or snow without this material.