Summary of AC interview:
He knows the climb very well as he's used it in his training rides since long time ago. As a junior he used to go by train in the morning rush hour from his parents home to the town at the foot of Puerto de Navacerrada, where he left his backpack in a bikeshop during his training rides.
Gradient is very steep and it requires climbing on the saddle to keep traction on the concrete sections (Surprising, as the video footage shows him out of the saddle most of the time) He uses a 36x28 gear in the steepest ramps. The climb from the Puerto de Navacerrada summit is just about 3.4km long, but with an elevation gain of almost 400m it can be compared to the hardest sections of Plan de Corones, Mortirolo or Angliru.
He also says something rather curious to me: he feels that he gets a better preparation by training high and sleeping low (I would say most people benefit from the opposite: train low and sleep high). So that's why he loves the area: he can sleep at home and then drive 1 hour by car to ride in the mountains.
The area is not what I would say really high for altitude training. The highest mountain passes around are between 1780 m and 1860 m, Bola del Mundo is at 2250 m and there are barely 12 km of continuous road always above 1800 m.
BTW, his voice sounds as if he's had a serious cold
