Walking around Viroinval and the Fondry des Chiens

A lovely and varied walk around Viroinval in Wallonia, with plenty to see, especially the spectacular Fondry des Chiens. UPDATED April 2026

Viroinval: A distinctive region

There is a corner of the south of Namur province that I drove through twice without stopping. I was on my way to somewhere else. I remember the road signs pointing to Nismes and the “Fondry des Chiens”. Something to do with dogs, I guessed; perhaps a dog’s hotel? The landscape was green and quietly dramatic. I made a mental note to come back one day and explore.

Well, I finally came back. After setting off early on a Saturday, I was parked up in the village of Nismes by 9.30 a.m. The village was deserted. I found a spot by the tiny tourist office, shouldered my backpack, and headed for Rue Grande to find the start of the trail. I had a 23-kilometre loop ahead of me, a full day’s walking through terrain that turned out to be quite unlike anywhere else in Belgium.

What makes this corner of the country so distinctive is geology. Viroinval sits at the meeting point of three very different landscapes: the schist and clay soils of the Fagne to the north, the limestone ridges of the Calestienne through the heart of the walk, and the forested slopes of the Ardennes to the south. Each has its own character, its own flora, its own ancient relationship with the people who have lived here. Walking this route is, in a very real sense, walking through deep time.

The route at a glance

Where on earth Is Viroinval?

Viroinval is a municipality in the province of Namur, formed in 1977 by merging eight villages: Dourbes, Mazée, Le Mesnil, Nismes, Oignies-en-Thiérache, Olloy-sur-Viroin, Treignes and Vierves-sur-Viroin. The name simply means Valley of the Viroin; the river that ties them all together. The total area is just under 121 square kilometres, with a population of around 5,700.

There is one geographical footnote worth knowing. Between 1995 and 2004, Viroinval held an improbable distinction. A monument in the village of Oignies-en-Thiérache marked it as the geographical centre of the European Union. This was when the EU had 15 Member States. When ten new countries joined in May 2004, the centre of gravity shifted east and the distinction passed on. The monument remains, a pleasingly obscure piece of Belgian trivia.

The Viroin river itself is formed a short distance away. Two streams – the Eau Noire (dark water, stained by peat) and the Eau Blanche (white water, filtering through limestone) – converge at a place called Roche à Lomme near Nismes. The contrast between the two rivers is not just poetic; it reflects the genuinely different geology on each bank.

The geology of the Calestienne

To understand what makes this walk special, it helps to understand the Calestienne. This is a narrow band of limestone country that runs across this part of southern Belgium, squeezed between the Fagne clays to the north and the Ardennes schist to the south. The limestone was laid down around 400 million years ago, when warm tropical seas covered the region, leaving behind vast beds of coral reef. What you walk across today is the floor of a Devonian ocean.

The result is a landscape quite unlike the rest of Wallonia: thin, warm, well-drained soils that dry out quickly in summer, creating conditions more typical of southern Europe than northern Belgium. The calcareous grasslands support rare orchids, and a number of continental and sub-Mediterranean plant species found almost nowhere else at this latitude. In summer, the insect life is extraordinary, with grasshoppers, fritillary butterflies and blue butterflies, some of them quite rare.

The limestone also does something dramatic underground: it dissolves. Rainwater, slightly acidified, eats through the rock over millennia, creating sinkholes, caves, and underground rivers. The Grottes de Neptune near Couvin are one product of this process. Le Fondry des Chiens (the first highlight on this walk) is another.

Le Fondry des Chiens

I did not have far to walk before my first eyebrow-raising experience. Just east of the village centre, the ground drops away without warning into one of the most extraordinary natural features in Belgium.

Le Fondry des Chiens is a sinkhole (a gouffre, in the local terminology) carved into a limestone reef. It is 100 metres long and up to 20 metres deep (some sources say 30 metres at the lowest point), its walls lined with jagged, rust-stained limestone and draped in ferns. You stand at the edge and look down into a long, dark chasm, the kind of place that would look perfectly at home in a fairy tale. In fact, the site has its own legend: a wandering knight who is said to haunt the gorge.

The name deserves some explanation. Fondry comes from the French fonderie: a smelting furnace. The chiens (dogs) is more contested. One theory holds that it refers to the Muslim warriors who, legend says, called the local population ‘infidel dogs’. Another simply says the site was used to drown stray dogs. Take your pick. (So nothing to do with a dog’s hotel!)

What is not in dispute is the human history. From the Iron Age through to the 19th century, iron ore was mined from the pits. The mining deepened the natural sinkholes and left the characteristic rust-red colouring still visible in the rock today. Since mineral extraction ended, the site has been declared a natural protected area and, since 2022, forms part of the Entre-Sambre-et-Meuse National Park.

A word of caution: accidents have happened here, particularly among people seeking the best selfie from the rim. There is no fencing. Enjoy the views, but keep a sensible distance from the edge.

The ecology within and around the Fondry is remarkable. The microclimate at the bottom of the chasm is cooler and more humid than the surrounding plateau, creating a refuge for shade-loving plants. On the limestone grassland above, the thin, warm soils support wild orchids, rare butterflies, and a flora that looks more Provençal than Belgian. May and June would be the best time for flowers. I have already made a note to come back.

Roche aux Faucons

Continuing along the plateau, the trail reaches a rocky outcrop known as the Roche aux Faucons (the Falcon Rock). The name is self-explanatory. It’s the kind of exposed limestone bluff where peregrine falcons have historically nested, and the viewpoint it provides over the surrounding forested valley is magnificent.

The woodland through this section is dense and beautiful. Beech, oak and hornbeam close in on either side of the path, with the understorey bright in spring with wood anemones and wild garlic. This is the kind of walking that reminds you why the Entre-Sambre-et-Meuse has been called the secret Ardennes. It’s less famous than the valleys further east, less crowded, and in my mind more quietly wonderful.

The abandoned limestone quarry

Further along the high ground, the path skirts the edge of a large abandoned limestone quarry. The drop is dramatic. A sheer face of pale grey rock falls away to the quarry floor below. And there is no fencing! A board at the site advertises it to rock climbers, for whom the bare limestone walls provide excellent training ground.

Quarrying has a long history in this region. The three valleys followed by the Three Valleys Steam Railway – the Eau Blanche, the Eau Noire and the Viroin – were economically important corridors for centuries. Stone, iron ore and timber extracted from the hills were transported out along the rivers and, later, the railway. Most of the stone buildings in the villages along this walk are built of locally quarried limestone, giving them their characteristic grey-and-pink colouring.

Do not get too close to the edge. The view is vertiginous and impressive; the ground is not always stable.

Olloy-sur-Viroin

After the drama of the high ground, the path drops down into the valley and the village of Olloy-sur-Viroin. This is roughly the halfway point on the walk. So it’s a good place to rest, fill a water bottle, and take stock.

Olloy is a picturesque riverside village, its stone houses running along both banks of the Viroin. The river here is wide enough to merit a proper bridge, and the reflections of the buildings in the water make it one of the more photogenic spots on the route. The village has a quiet, lived-in quality. This is not a tourist village, just a real one.

The Three Valleys Steam Railway passes through Olloy, making it possible to combine a section of this walk with a ride on the heritage line between Mariembourg and Treignes. The railway was built in the early 20th century and operated as a passenger service until 1963. It was then preserved as a heritage railway in 1973, and now runs on a 14-kilometre stretch of standard-gauge track. It’s an unusual and enjoyable way to see the landscape.

Vierves-sur-Viroin: One of Wallonia’s most beautiful villages

The route continues through the valley before climbing again to reach Vierves-sur-Viroin. This is officially one of the 32 Most Beautiful Villages of Wallonia, and I could see why it has earned this designation.

The village is built on a hillside above the Viroin, its streets and alleys cascading downward in a way that does, as the guidebooks promise, give it a distinctly Mediterranean atmosphere. The stone houses are compact and tightly packed, the lanes steep, and the whole effect (particularly on a warm summer afternoon) is of somewhere further south than it has any right to be. The Viroin winds clear and calm through the meadows below.

The village is dominated by the Château des Comtes de Hamal, a medieval fortress remodelled in classical style over the centuries. It is private property, but it can be admired from the village.

Vierves is also the headquarters of the Cercles des Naturalistes de Belgique, making it a centre of gravity for nature guides, training courses, and ecological initiatives in the Entre-Sambre-et-Meuse. And once a year in February, the village erupts in carnival, climaxing with the burning of a giant straw figure (the bonhomme hiver, the man of winter) in the village square.

The Return: Forests, meadows and more rock

From Vierves, the route swings back towards Nismes through a landscape that shifts in character one final time. The path enters deep, mixed woodland. Firstly beech and oak, and then darker conifer stands. This is the Ardennes beginning to make its presence felt on the southern edge of the Calestienne.

The forest opens onto fields and more limestone outcrops, and the final kilometres back to Nismes include a succession of smaller rock formations that close out the geological story of the day.

By the time the village comes into view, you will have walked through coral reef, iron age mine workings, medieval castle grounds, and the oldest forests in southern Namur. Not bad for a day’s walking.

The disaster (a cautionary tale)

I should tell you what happened when I returned to Nismes at 5.30 in the afternoon.

Walking back through the village after 24 kilometres, the sound of music reached me. A summer market was in full swing. Scores of stalls filled the streets, which had been made pedestrian-only. And my car (parked that morning by the tourist office) was completely imprisoned behind racks of women’s clothing.

The stall owner was sympathetic but firm. Everyone in the village had known the market was happening. Cars were supposed to be removed before noon. He could not move his racks. The market would finish at midnight; I could collect my car at 1 a.m.

I had a B&B booked. In Dourbes. Five kilometres away.

I retrieved my overnight bag from the car and walked. Which is, I suppose, entirely in keeping with the spirit of the day.

The lesson: if you are visiting Nismes on a Saturday in summer, check the local events calendar before deciding where to park. The village hosts a popular seasonal market, and the tourist office will have details.

Where to stay around Viroinval

I ended up at Les Gabelous, a B&B in the neighbouring village of Dourbes. Despite the unplanned five-kilometre approach march, it turned out to be a super B&B. Hosts Fabienne and Ben (since then there has been a change of management) were warm and welcoming; the facilities were excellent; the food (evening meal, breakfast, and a packed lunch) was wholesome, generous and good value. And in the morning, Ben drove me back to Nismes to collect my liberated car.

If you are planning to stay in the area around Viroinval, this is a very good base. Dourbes is itself a pretty village, and the surrounding countryside gives you easy access to the full range of Viroinval walks. Other accommodation nearby includes:

• La Cle des Sens: “A beautiful little bed and breakfast, walking distance from the station and the steam train yard. I very much hope I can visit again.”
• La Chocolaterie: “Tranquil setting. Beautiful gardens. High quality furniture and decor. Very confortable bed. Delicious breakfast.”

Practical information

Getting to Viroinval

Nismes is approximately 130 km from Brussels, via the E40 and then south towards Couvin. There is no direct rail connection; the nearest SNCB station is Mariembourg, from which the Three Valleys Steam Railway runs a seasonal heritage service through to Treignes, stopping at Nismes.

Route download

The map of my Viroinval walk is shown below. You can download the map as a PDF. And you can get the GPX route from my RouteYou page.

Parking

There is parking near the church and tourist office in Nismes. If you are visiting on a Saturday in summer, check in advance whether a market is being held. If so, use a different car park to avoid the situation described above.

Footwear

Sturdy walking boots are recommended. The limestone sections can be slippery when wet, and some stretches involve significant ascent. The path into Le Fondry des Chiens itself is steep and uneven.

Visiting Le Fondry des Chiens

The site is open year-round and free of charge. Note that it may fall within hunting grounds between October and December; check locally before visiting in those months. Keep children and dogs under close supervision near the rim.

Also worth visiting near Viroinval

• Three Valleys Steam Railway: A wonderful heritage railway running 14 km through the Fagne, Calestienne and Ardennes. Stops include Nismes, Olloy-sur-Viroin, Vierves-sur-Viroin and Treignes.
• Musée du Malgré-Tout, Treignes: An excellent regional archaeology museum covering prehistory through to the industrial era. See museedumalgretout.be
• Espace Arthur Masson, Treignes: An old-fashioned school experience dedicated to the regional writer Arthur Masson, creator of the much-loved Ardennes character Toine Culot. See espacemasson.be
• Écomusée du Viroin, Treignes: A living museum of traditional crafts and rural life. See ecomusee-du-viroin.be
• Grottes de Neptune, Couvin: Spectacular underground river caves just up the road, where the Eau Noire disappears underground before re-emerging near Nismes.
• Vierves-sur-Viroin village walk: The Most Beautiful Villages association has a self-guided discovery trail with interpretive boards starting from the church. Allow an hour.

Frequently Asked Questions

How difficult is the walk around Viroinval?

The walk is rated moderate. The total distance is 23 km with around 400 m of ascent and descent. There are some steep sections, particularly around Le Fondry des Chiens and the climb to Roche aux Faucons. It is not a technical walk, but you should be comfortable covering longer distances on uneven ground. Allow a full day — six to eight hours including stops.

Can I do a shorter version?

Yes. The first section to Le Fondry des Chiens and back to Nismes is a popular 4-km walk that the tourist office in Nismes signposts as a family-friendly route. You can also break the full loop by taking the Three Valleys Steam Railway from Olloy-sur-Viroin or Vierves-sur-Viroin back towards Nismes (seasonal; check timetables).

What is the best time of year to walk this route?

April to October is the main walking season. May and June are particularly rewarding for the orchids and wildflowers on the calcareous grasslands around Le Fondry des Chiens. Summer brings long days and warm temperatures. Autumn turns the forests gold. In winter, the paths can be muddy and sections of the site fall within hunting grounds (October–December).

What is Le Fondry des Chiens?

Le Fondry des Chiens is a natural limestone sinkhole (a gouffre) located just east of Nismes. It is 100 metres long and up to 20 metres deep, formed by millennia of acid rainwater dissolving the Devonian limestone beneath the plateau. From the Iron Age to the 19th century, it was mined for iron ore. Today it is a protected nature reserve known for its rare flora, including wild orchids and globularia, and its unique microclimate.

Is the Fondry des Chiens suitable for children?

The surrounding trails are accessible to older children and families. The gorge rim itself is unfenced, however, and requires close supervision of young children. Several accidents have occurred at the site. Keep a safe distance from the edge.

Are there cafés or restaurants along the route?

Nismes has café and restaurant options near the start and finish. Olloy-sur-Viroin has limited facilities; it is worth checking what is open before you go. Vierves-sur-Viroin has a restaurant (Le Petit Ménil) which serves local produce and has hotel rooms if you wish to stay the night.

Can I arrive in Viroinval by public transport?

The nearest main-line station is Mariembourg (SNCB/NMBS). From there, the Three Valleys Steam Railway runs a seasonal heritage service to Nismes, Olloy-sur-Viroin, Vierves-sur-Viroin and Treignes. This is not a commuter service. There is also a TEC bus service (line 60/3) connecting Viroinval with other villages in the valley.

A final thought

The Viroin valley is the kind of place that takes a little effort to reach, and rewards that effort with something genuinely rare: a landscape that feels completely itself. The geology is unlike anywhere else in Belgium. The villages have not been prettified for visitors. The walking is serious enough to earn your supper but varied enough to keep you interested all day.

I came back the next morning to collect my car. The market was long gone, and Nismes was quiet again in the early light. Heading out of the village, I already had a feeling I would return. The Viroin valley has a way of doing that to people.

If you have walked this route or somewhere else in Viroinval, or if you have questions, I would love to hear from you in the comments below.

Denzil Walton

I created Discovering Belgium in 2011 to share the country’s hidden stories, fascinating places, and remarkable people. Through articles, photography, and audio walks, I share discoveries that reveal Belgium beyond the obvious. Hope you enjoy this site.