D428 is a balcony road through Vallon de Pierlas
Vallon de Pierlas is the name of a very scenic valley located in the Alpes-Maritimes department, in the Provence-Alpes-Côte d'Azur region of southeastern France. It's one of the famous French balcony roads.
The road through the valley is totally paved, with countless hairpin turns dug into the rock. It’s called D428. The road is 7.3km (4.53 miles) long, running from Pierlas to D28 road (Gorges du Cians). The road has some narrow parts, so proceed cautiously and hope no other vehicles come from the other direction. Not recommended if you don't know how to reverse.
It features very steep sections, hitting a 26% of maximum gradient through some of the ramps. The elevation gain is 542 m and the average gradient is 7.42%. Not recommended to beginner riders. The road is closed to heavier vehicles. A balcony road is a hair-raising lane cut into the sides of sheer cliffs. It’s a kind of road not for those who fear heights. There is little room for error on these roads. It’s normal for your palms to sweat looking at those photos, imagine what it must have been like before the barriers.