Puerto del Reventón

Puerto del Reventón is a mountain pass in the Sierra de Guadarrama, sitting on the border between the provinces of Madrid and Segovia at an elevation of 2,039 meters. It connects the Lozoya valley on the Madrid side, near the town of Rascafría, with La Granja de San Ildefonso on the Segovia side. It's one of the higher passes in this stretch of the Sistema Central and a popular waypoint for hikers and mountain bikers within Sierra de Guadarrama National Park.

How do you get there?

Most people start from Rascafría, following the marked RV-4 (green) and PR-10 trails. The route begins near the sports complex in Rascafría, running first along a forest track before turning onto a mountain path toward a spot known as Carro del Diablo, then climbing steadily to the pass itself. Coming from the other direction, La Granja de San Ildefonso offers a shorter approach, though it still involves a sustained climb. Mountain bikers often extend the ride into a longer loop through Puerto de los Cotos and Puerto de los Neveros.

What will you see?

The full crossing runs roughly 16–17 km depending on the exact route chosen, with about 900 meters of elevation gain — demanding, but laid out without especially steep sections. Spanish kings historically used this same route to travel between Madrid and their summer residence at La Granja. Along the way, the trail passes through pine forest, open mountain meadows, and the rocky terrain typical of the Guadarrama range, and the pass itself offers views down both sides of the mountains — the Lozoya valley on one side and the Segovia countryside on the other. The route connects into a wider network of trails that also takes in the Chorro Grande waterfall and the neighboring Puerto de los Neveros pass.

When should you visit?

Late spring through early autumn (roughly May to October) is the best window, once snow has cleared and temperatures at over 2,000 meters are manageable. In winter and early spring, snow tends to settle on the pass, making the crossing longer and requiring proper winter gear. Because the route is heavily exposed to sun and wind, it's worth setting off early to be back down before the afternoon thunderstorms that are common in the Sistema Central during summer.

How long does it take?

Completing the full crossing from Rascafría to La Granja de San Ildefonso typically takes around 5 hours — about 3 hours climbing and 2 hours descending. Hikers who only want to reach the pass and return the same way should still budget several hours, as it remains a demanding outing even as an out-and-back trip.

Frequently asked questions

Is this route suitable for beginners? Not really — the elevation gain and altitude above 2,000 meters call for good fitness and mountain hiking experience. Beginners are better off sticking to the shorter, lower sections of the valley.

Can you cross the pass by bike? Yes, it's a well-known mountain biking route, often combined with the nearby Puerto de los Cotos and Puerto de los Neveros passes into longer loops of over 50 km.

How high is the pass? Puerto del Reventón sits at 2,039 meters above sea level, making it one of the higher passes in the Sierra de Guadarrama.

Are there other attractions nearby? Yes — the Chorro Grande waterfall is close by, along with the historic town of La Granja de San Ildefonso and its royal palace, plus the Lozoya valley on the Madrid side.