You could call the climb to Alpe d’Huez the world’s first purpose-built cycling climb.

Initially built for cars, but perfect for cyclists. Built around 1936 to improve access to the expanding ski resort at the top of the mountain. The average percentage is relatively high at 8.1%, with a length of 13.2 km and 1,071m. of altitude again. Which isn’t, on paper, one of the most challenging climbs.
However, what Alpe d’Huez lacks in altitude and length is made up for in intensity. The climb is full-on from the bottom to the top, with little respite from the infernal gradient or the heat bouncing off the south-facing, rock-lined road. The weather and temperature don’t change from top to bottom, and no altitude kicks in, so riders have no reason not to go for it. Which they do.

The climb has no gentle run-in, so the start is brutal.
Starting at Le Bourg d’Oisans, going from 0% gradient to 10% average straight up from the Romanche valley floor, continuing in this vein for the first 2.6 kilometres. It’s imperative not to go too hard in this first section. Otherwise, you will pay further up the climb. As someone once said, “Start like a galloping horse, finish like a nodding donkey”.