Bouillon is squeezed into a tight loop of the river Semois, with a castle that seems to grow out of the rock above the town. The crags force the river into a hairpin, and the town huddles on the neck of land below. It is a small place, barely five thousand people, yet it is one of the most memorable in the Belgian Ardennes, and the bend of the Semois here is the kind of scene that makes people take out their phones without being asked.
The castle is the star. Its origins reach back to the eighth century, and in the late eleventh century it belonged to Godfrey of Bouillon, who sold or mortgaged his lands to help fund the First Crusade and went on to become the first ruler of Jerusalem under Latin control. A statue of him stands in the square. The fortress was later reshaped by Vauban, Louis XIV's great military engineer, and you can walk its long ramparts and dungeons. In summer there are falconry displays.
The riding around Bouillon is some of the best in southern Belgium. The roads follow the Semois through steep, wooded meanders, with tight bends, a short climb and a drop around each spur, and the tobacco-drying barns in the villages are a sign that this was once a tobacco-growing valley. The surface varies from excellent to patchy, and in autumn the leaf litter and morning mist make the shady corners treacherous. Weekends are busy with canoeists, cyclists and motorbikes alike, so a weekday ride is calmer.
There are fuel stations on the approaches, though in the smaller villages upriver you will not find any, so top up in town. Cafes around the bridge serve waffles and Ardennes ham, and local trout is on many menus. Give yourself time to walk across the old bridge for the view of the castle, then take the road towards Corbion or Sedan for the best bends.
Bring a jacket: the valley holds cool air even in summer, and rain arrives quickly off the high plateau.