A cobbled sector does not feel like a rough road. It feels like the bike is trying to get away from you, and the only thing that makes it stop is going faster, which is the cruel joke at the middle of Paris-Roubaix.
These stones were never laid for looks. They are field roads between beet and wheat, put down a century ago because it was the cheapest way to stop a cart sinking, and largely left alone since. The Trouée d'Arenberg runs dead straight for two and a quarter kilometres through the forest at Wallers and tilts very slightly downhill, so riders reach it at nearly fifty kilometres an hour with the race already fighting. Mons-en-Pévèle and the Carrefour de l'Arbre come at kilometre 210 and 241, when there is nothing left to fight with.
You can ride every one of them on an ordinary Sunday. Most people only do it once.