This is another critical day for the GC contenders and another that is treading on new ground in the mountains. There are four first-category climbs on the menu, with the Puerto del Acebo as the main focus because it is tackled twice, the second time continuing beyond the pass to reach the monastery that lies 200 vertical metres above it.

The stage starts in western Asturias in Tineo and heads south-west to Cangas del Narcea for the first ascent of the Acebo. Averaging seven per cent for 8km, there are frequent changes of gradient, with long stretches close to double figures. After descending very quickly back to Cangas del Narcea, the route heads south-west again to start a big loop at La Regla.

Two of the region's best known climbs feature on this loop, both regular features in the Tour of Asturias stage race. First up is the Puerto del Connio, almost 12km at 6.2 per cent, with the gradient only a fluctuating a little either side of that mark, which will suit the grimpeurs-rouleurs like Primoz Roglic and Rigoberto Urán. At 1,315 metres, this summit is the stage's highest point.

After dropping into the valley beyond, the riders soon start to ascend the intriguingly named Puerto del Pozo de las Mujeres Muertas, which has nothing to do with dead women but is actually a mistranslation into Castilian Spanish of an Asturian phrase describing local rock formations. Similar in distance and gradient to the Connio, it's much more irregular, steep at the bottom and again near the top, with a plateau in the middle.

The riders will drop down to La Regla and continue back to Cangas del Narcea to climb to the finish at the Santuario del Acebo. They come at it from the much steeper side of the pass that they descended earlier in the day. Averaging 9.7 per cent for 8km, it begins fiercely, eases off after 1,500 metres, then kicks up steeply again for 2.5km before evening out to a steady nine per cent for the final 3.5k.