Alto de l’Angliru (also known as Gramonal) is one of the most famous mountains passes in the sport, and one of the most demanding: 12.2 kilometers at an incredible 10.2%, grading out at a maximum of 23.5% not far from the top.

Starting at Santa Eulalia, the ascent is 17.7 km long. Over this distance, the elevation gain is 1.403 meters. The average percentage is 7.9 %. And starting at La Vega, the ascent is 12.55 km long. Over this distance, the elevation gain is 1.248 meters. The average percentage is 9.9 %. It is arguably one of the most demanding climbs in professional road bicycle racing, having been climbed the first time in the Vuelta in 1999. The last half of the climb, from the six-kilometre mark to the summit, the average gradient is 13.1%. The steepest part, which has a 23.6% slope, is known as Cueña les Cabres and is located about 3 kilometres from the summit. The climb is no easier from this point, as there are two later ramps at gradients of 18 to 21%.

gravel portions look ok on google satellite view

Dangerousroads.org