The tough part is the first kilometre. The N5 is one of those fast, wide pre-autoroute highways, connecting the south with Brussels. It sweeps uphill from the town of Couvin, which sits astride the Eau Noire, an appropriately tranquil river. The town's surroundings are full of interest: a warren of caves lacing through a limestone escarpment, folds of forest draped over waves of hills that roll towards the French border; and even the hamlet, Brûly-de-Pesche, from which Hitler directed wartime operations in the critical summer of 1940. But for the best little bike ride in western Wallonia, you have initially to head away from your ultimate target, Chimay, and endure whoosh after whoosh of lorry as you scuttle north.

Soon, though, the escape route appears to your left. This is a steep ascent, over the railway line then climbing towards a ridge. Get off and walk, by all means; a keen cyclist could cover this 18km meander in an hour, but much better to make a morning or afternoon of it.

After shrugging off a few new-built houses, you are deep in la Belgique profonde. The road, which goes by the number of the D939, quietly swerves between woodland and meadow, village and valley. The first settlement of any size is Boussu-en-Fagne, Fagne referring to this lovely patch of countryside. A figure of Jesus stands sentinel beside the road, pointing towards a row of slate-grey houses.

Even on an overcast day, the landscape takes on a monochromatic beauty: a delicate pencil sketch of hedgerows, crops and trees. It gets better; while climbing to shrug off the trucks and townscape, you also cross into another valley. After the Eau Noire comes the Eau Blanche - a young, fast-flowing tributary. Not quite the white-water rapids that its name suggests, but capable of carving a course through south-west Belgium.

You swoop through Dailly (no reason that I could see to dally) then down to the river. On the far side, the road climbs steeply to a forlorn church. You, and the road, are into your stride now: it follows a ridge, giving grand views to either side.

After one kilometre or so, you cross into the province of Hainaut - and start to descend to the most appealing village along the way, Lompret; see page VI for a good place to stay. To find your way into the village, and through to your final destination, Chimay, disregard all the signs for Chimay. You should begin by bearing left at a junction into the village, arranged prettily around the river. When invited, by a sign to Chimay, to turn left across the bridge, decline and follow the curve along the north side of the river, flanked with cottages, until it guides you across the Eau Blanche. (At this stage, following any signs to Vaulx is a good plan). You then make your final ascent, the most rewarding of all, because it should set you spinning along the most dramatic ridge. At the T-junction, ignore the sign for Vaulx and go right for what seems rather too long in the direction of nowhere in particular. Just as you suspect you have gone wrong you should cross a highway and be directed into the centre of Chimay.

The grand finale is the chateau, which you deserve to visit (guided tours only) as a treat, before awarding yourself a Chimay beer. But if you feel the need for a little more cycling, may I recommend Highway 99? This is not quite Belgium's equivalent of Route 66, but it is a superbly engineered 15km sprint to the French border - and surprisingly free of trucks.

Simon Calder paid £59 for a return ticket from London on Eurostar. He travelled out via Brussels and Charleroi to Couvin.