Choosing where to start and pressing the START button on the watch to officially begin this FKT was not an easy decision.
In 2021, I climbed and descended Cerro Arenas for the first time from Puente La Engorda, solo, in about 8 hours roundtrip. It was probably also the first ascent done in a mountain running style and in a single push. That time, I entered without permission, crossing the gate at dawn as a form of protest against the valley’s administration.By then, the valley had already been acquired by its current owners, who also had ties to Alto Maipo. I remember a talk in 2018 at the climbing gym where I used to teach, where they explained that the purchase was for conservation purposes and that they would never charge for access. However, as soon as they took control, things didn’t turn out as promised.
The idea that such an important valley, for climbers, mountaineers, skiers, and for the local community, could become private property is unsettling. And for good reason: doubts were always there, especially regarding the impact on local communities and access to historic climbing areas. On top of that, there’s Alto Maipo’s long history of intervention in the area, which has consistently put free access to the mountains at risk.
Now, in 2026, I decided to officially register this FKT. And while I would have preferred to do it outside the system, as a form of protest against fees and the lack of infrastructure, services, or maintenance, there is something that weighs more: respect for the rules.
Because even though I don’t agree with paying for access to the mountains under these conditions, I do believe that, when done properly, an entrance fee should reflect conservation efforts, education, and support for local communities. If that were the case, many of us—including myself—would gladly pay. But unfortunately, that’s not the situation here.
Still, following the Fastest Known Time rules is mandatory. Not only for legal reasons, but also for ethical ones: if we want others to repeat this route and this FKT, we all have to play under the same conditions. So the invitation is clear: anyone who wants to attempt it should do so properly, with permission and by paying the entrance fee, even if we don’t agree with it.
For this project, I invited Felipe. Weeks earlier, while we were climbing at Pared de Jabbah, he saw Arenas for the first time from that perspective. Just mentioning the idea was enough to get him motivated immediately.
We decided to start from the upper parking area, Mirador del Volcán, since it’s the last point accessible by car. To get there, you have to pay CLP $10,000 per vehicle, plus CLP $5,000 per person. It’s not insignificant, but at least it allows you to avoid several kilometers of rough vehicle track that add nothing real to the running experience.
From the pole with the chain, touching it, we started and finished the route.
The mountain is simply spectacular: technical for running, wild, vertical, relentless. River crossings, loose terrain, and a powerful Andean environment. Pure mountain running.
Our goal was to complete the round trip in about 7 hours. The surprise was huge when we managed to do it in 5 hours and 9 minutes.
On the descent, we took some variations. The ascent route has a lot of loose material, and we had already had several close calls with rockfall triggered by our own movement. Changing lines while descending was necessary to move more safely and fluidly.
A big, beautiful, and demanding mountain. A perfect place to step into the 4,000 meter range and run far away from everything.
Total: 05 hours 09 minutes 13 seconds. 13,16 kilometers. 4.366 meters.