The 15th stage of the Vuelta is set to be a nightmare not just for sprinters, but also for climbers themselves. In this 142-kilometer stage, the finish is at the top of the Cuitu Negru in Valgrande-Pajares, a truly monstrous climb. The asphalt road to the summit was specially built for the Vuelta just under fifteen years ago.

The stage begins on Sunday in Infiesto, a small village with a typical old church, like many others in the region. From Infiesto, the peloton will move along rolling roads toward three climbs that precede the Cuitu Negru. Two of these climbs are of first category, and one is of third category.

After 28 kilometers, the peloton starts the Alto de la Colladiella (7.8 km at 7.1 percent), followed soon after by the Alto de Santo Emiliano (5.4 km at 5.6 percent). As a warm-up, the peloton will tackle the Alto de la Colladiella once more after 80 kilometers.

At this point, there are about 37 kilometers to the base of the Cuitu Negru. After a long descent, the peloton arrives in Puente de Fierros, where the final climb of 19.5 kilometers up the Cuitu Negru (19.5 km at 5.2 percent) begins.

The average gradient of this climb is somewhat misleading: the first seven kilometers are relatively easy, but the difficulty ramps up significantly afterward. At eight kilometers from the summit, the gradient rises to 11 percent, and it becomes progressively steeper. The final 2.5 kilometers are particularly brutal, with gradients exceeding 12 percent and reaching up to 24 percent just below the summit.

This climb could lead to significant time gaps. In 2012, when Dario Cataldo won at Cuitu Negru, Joaquim Rodriguez gained over two minutes on major rivals Alejandro Valverde, Chris Froome, and Alberto Contador.