You see it long before you understand it. From the road below Duilhac, Peyrepertuse looks like part of the mountain: a grey ridge of limestone with walls grown along its spine, so long and thin that people compare it to a stone ship. Up close it is two castles in one. The lower fortress on the eastern end is older, and at the western summit stands the keep of Sant Jordi, added by the French crown after Louis IX took control of the Corbières in the mid-thirteenth century. The site sits around 800 metres up, and the climb from the car park is short but steep, on a rocky path that is no fun in stiff motorcycle boots, so bring trainers if you can.
These fortresses are usually sold as Cathar castles, and the Cathars did shelter in this country during the Albigensian Crusade, but what you see is largely royal French work, built to guard the border with Aragon. When the Treaty of the Pyrenees moved the frontier south in 1659, places like this lost their purpose and slowly emptied. Standing on the walls you can see why they mattered: the Fenouillèdes to the south, Quéribus on its own crag, and on clear days the Mediterranean and the snowy bulk of the Canigou.
The riding nearby is outstanding. The classic approach is from Saint-Paul-de-Fenouillet through the Gorges de Galamus, a road cut into the cliff face above a deep, narrow canyon; it is single-lane in places, with a stone parapet and oncoming cars, and in summer there are often traffic controls. Take it slowly and enjoy the drop. Beyond, the D14 through Cubières and Duilhac winds through scrub, vines and rock, and the run east towards Cucugnan and Quéribus is a joy of short straights and tight bends.
The wind deserves respect. The tramontane comes down hard from the northwest and can push a bike around on the ridges, and the castle walls get properly blustery. Go early in summer before the heat and the coaches arrive; late afternoon light on the stone is lovely too. Fuel is the thing to plan: Saint-Paul-de-Fenouillet is the nearest town with pumps, otherwise Estagel or Ille-sur-Têt. Duilhac has a café or two, and the local reds, Corbières and the sweet wines of Maury, are for the evening, not the ride.