Nismes and its geological phenomena

Over millions of years, the action of water has carved huge chasms up to 20 metres deep into the limestone. These natural chasms are called "Fondrys". In Belgium, they are only found in the Viroin region. Discover geological curiosities and viewpoints. Explore beautiful landscapes combining rocks, rivers and limestone grasslands where numerous orchids appear in spring.

Details

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  • Walking
    Activity: Walking
  • ↔
    Distance: 15.74 km
  • ◔
    Average duration: 5h 45 
  • ▲
    Difficulty: Moderate

  • ⚐
    Back to start: Yes
  • ↗
    Ascent: + 440 m
  • ↘
    Descent: - 441 m

  • ▲
    Highest point: 231 m
  • ▼
    Lowest point: 145 m

Photos

Description of the walk

The term "Viroinval" is a variant of "vallée du Viroin", the most important river in the municipality. It does not therefore refer to a specific location. Our hike starts in Nismes, the administrative centre of Viroinval.
Parking is available in the streets near the church in Nismes.

(S/E) With your back to the church, take the road opposite, to the right of the Eau Noire, towards the Tourist Office. Pass it and, further on, turn left into Rue d'Avignon to see the resurgence and the cave. Retrace your steps. Turn left and climb the steps of the Bailli's house. At the end of the forecourt, turn left. Go up the street and, when you reach the tower, go up the stairs on your left. At the fork, turn left and go up the stairs again. At the end of the stairs, continue climbing. At the next fork, turn left to discover the view of Nismes. Retrace your steps and turn left. At the fork, turn right.

(1) At the forest path on the left, continue straight ahead. At the crossroads, you will see benches and Le Matricolo on your right.

(2) Return to the crossroads and take the path opposite (the path that was on your left when you arrived). At the end of the path, turn right and then take the next path on the left. At the fork, follow the path on the left. When you reach the stairs, go down them. At the bottom, you will arrive at the road with a calvary on your right. Continue straight ahead to cross the bridge over the Eau Noire.

(3) Continue along the road opposite. At the end, turn left, then take the first road on the right (Rue Orgeveau). Go uphill. Take the path between two new buildings, after number 14. A lamppost marks the entrance. Continue along the path on the left, passing behind the gardens. At the top, turn left. A path joins you on your right; continue straight ahead.

At the end of the woods, turn right onto the stony path. At the end of this path is the Fondry des Chiens. To enter the Fondry, go around to the right, staying as close as possible to the Fondry. As you descend towards the entrance, you will see a narrower Fondry on your right, just behind the barriers.

(4) At the same height as these, on your left, is the entrance to the Fondry des Chiens. Go in to explore the cavities and caves, but do not climb! Come back out and turn left. Follow the Fondry and, at the end, take the path downhill on your right. Follow the fence on your right. Join a path and turn right.

(5) Go through the gate and follow the path. Follow the hedge and go up towards Les Abannets.

(6) Turn right. Keep to the right when you come to a path and then another. Go under the trees. Follow the path to the viewpoint.

(7) To reach Roche Trouée, look for the path descending to your left but to the right of the rocks and descend carefully. The path is very difficult, especially if it has rained, and almost invisible if the vegetation is dense. Find the opening and then climb back up. Take the same path as on the way there until you reach the first fork. Turn right. Keep right until you reach the bottom of La Tienne (hill). Turn left and pass a group of rocks. Follow the fence and then climb back up the path with your back to the road and alongside the woods.

(6) At the crossroads, ignore the path entering the forest and continue straight ahead on the opposite route from the outward journey to reach the crossroads at the barrier.

(5) Immediately after the barrier, take the path on your right. Follow the fence, then turn left and head towards the edge of the woods. With the trees on your right and the limestone lawn on your left, climb uphill. At the top, follow the path furthest to the right, at the edge of the woods. Climb up to the road.

(8) Turn right. At the intersection, turn left and continue right at the fork. Stay on the path until you reach Roche aux Faucons. Continue to the viewpoint.

(9) From the Roche aux Faucons viewpoint, retrace your steps to the forest path and continue along it, now on your right. Follow this path to the T-junction.

(10) Go down the path on your right. Go down to the railway tracks, using the stairs if you wish.

(11) Cross with caution, as this line is still in use for steam trains. Go down the steps and follow the path along the Viroin. It quickly moves away from the river and, further on, runs alongside meadows at the edge of the woods. Don't worry about the paths that join you, stay on the main path and leave the woods.

(12) At the crossroads on the right, cross the bridge and turn left. After the rocky outcrop and the two stone houses next to each other, turn right onto the path running alongside the gable. Then turn right onto the path leading up to the castle ruins.

(13) At the top, turn right to see the ruins. Be careful not to climb on them. Retrace your steps and continue along the path on your right. At the fork, turn left. Pass the Haute Roche viewpoint.

(14) Take the path again and continue straight ahead at the crossroads and the next one too. Then, at the start of the rocks, you have two choices: either take the path down to the bottom of the rocks (a tricky passage) and then pass below the climbing site, or take the path to the right of the rocks and follow them, keeping to your left, to pass between two rocky outcrops and descend after the climbing site. Continue down the path on the right. At the river, turn right and return to the bridge, which you cross again.

(12) At the end, turn right and take the right at the barrier. Further down, turn left. Stay on the forest track, which then becomes a path. At the railway line, take the path on the left just before the river bridge and its red railing.

(15) Cross the railway line with caution and continue straight ahead. At the fork, turn right and then left at the next fork. Go uphill. At the forest track, turn right. At the crossroads, continue straight ahead and turn left at the fork.

(16) At the paved road, turn right and immediately turn onto the leftmost path.
Follow the path to the stairs, go down them, cross the bridge and return to the car park (S/E).

Waypoints

  1. S/E : km 0 - alt. 156 m - Église Saint-Lambert (Nismes)
  2. 1 : km 1.03 - alt. 224 m - Forest path
  3. 2 : km 1.23 - alt. 219 m - Matricolo
  4. 3 : km 2.06 - alt. 157 m - Bridge over the - Eau Noire (rivière) - Belgique
  5. 4 : km 2.98 - alt. 213 m - Fondry des Chiens
  6. 5 : km 3.37 - alt. 198 m - Barrier
  7. 6 : km 3.63 - alt. 204 m - Les Abannets
  8. 7 : km 4.06 - alt. 192 m - La Roche Trouée
  9. 8 : km 5.5 - alt. 219 m - Road
  10. 9 : km 7.1 - alt. 174 m - Roche aux Faucons
  11. 10 : km 7.49 - alt. 215 m - Downhill trail
  12. 11 : km 7.78 - alt. 152 m - Railway crossing
  13. 12 : km 9.34 - alt. 149 m - Dourbes crossroads - Viroin (rivière) - Belgique
  14. 13 : km 10.2 - alt. 213 m - Château de Haute Roche
  15. 14 : km 10.4 - alt. 219 m - Haute Roche
  16. 15 : km 13.36 - alt. 159 m - Railway crossing
  17. 16 : km 15.01 - alt. 207 m - Road
  18. S/E : km 15.74 - alt. 156 m - Église Saint-Lambert (Nismes)

Notes

From October to January, remember to check the hunting dates.
The cobblestones are very slippery in wet weather, near the tower at the very beginning of the hike.
The route may vary slightly depending on the maintenance of the limestone grasslands by sheep grazing. In this case, removable barriers will be installed. Simply follow them to find the trail.
It is best to visit when there is no foliage so that you can appreciate the fondrys.
May is the best month to see orchids on the limestone grasslands.
La Roche Trouée is accessible via a steep, fairly difficult path that is invisible when the vegetation is too high.
There is a tricky section on the descent near the climbing rocks after the (14), especially in wet weather.
There is no drinking water along the route.
Muddy and slippery sections in wet weather.
Benches: at Matricolo (2), at the end of the Matricolo descent trail, at the arrival point at Fondry des Chiens, at Haute Roche (14)
Picnic table at the rocky outcrop in Dourbes after the (12)

Worth a visit

During

Resurgence of the Eau Noire: part of the river disappears into the Grottes de Neptune (Couvin) and reappears at Nismes. Today, this resurgence is a secondary branch of the Eau Noire.
Grotte du Pont d'Avignon: a shelter for bats, not open to visitors
Matricolo: a natural chasm exploited as a quarry in the last century, it is the largest in the region but less spectacular than the Fondry des Chiens.
Fondry des Chiens: a huge chasm, up to 20 metres deep.
Point de vue de la Roche Trouée: A large gaping hole characterises this rocky outcrop through which a river once flowed.
Les Abannets: water has formed countless caves and caverns in the underground limestone. The caves on the plateau are not open to the public.
la Roche aux Faucons: viewpoint over the village of Olloy sur Viroin
Ruins of Dourbes Castle
Haute Roche: viewpoint over Dourbes

Near
Jardin d'O de Nismes
Brasserie des Fagnes in Mariembourg
Three Valleys Steam Railway, Mariembourg - Treignes
Neptune's Cave, Couvin

Reviews and comments

4.5 / 5
Based on 39 reviews

Reliability of the description
4.4 / 5
Ease of following the route
4.5 / 5
Route interest
4.8 / 5
Pegase
Pegase

Overall rating : 4 / 5

Date of your route : Nov 03, 2025
Reliability of the description : ★★★☆☆ Average
Ease of following the route : ★★★★☆ Good
Route interest : ★★★★★ Very good
Very busy route : No

Beautiful route, but the description is somewhat vague at times, especially after the matricolo point and after the Fondry des chiens. Point 1 is uninteresting, and at the viewpoint, the view is blocked by trees.

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GuyLeroy
GuyLeroy
• Edited:

Overall rating : 5 / 5

Date of your route : Jun 25, 2025
Reliability of the description : ★★★★★ Very good
Ease of following the route : ★★★★★ Very good
Route interest : ★★★★★ Very good
Very busy route : No

A beautiful route that we highly recommend. Very varied, with views, forest, river, a series of climbs that remind you that you are in the mountains, quite a few long straights, almost no paved roads, points of interest such as Fondry des Chiens, Roche aux Faucons, Haute Roche and its castle.
Two points:
-la Roche Trouée is not worth the detour in our opinion and is very close to a very noisy road
-be careful after point 16, turn right, then immediately left, and there is no path at the moment because there is a sheep pen. Follow the fence to find the path further on.

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User 13190952
• Edited:

Overall rating : 5 / 5

Date of your route : May 19, 2025
Reliability of the description : ★★★★★ Very good
Ease of following the route : ★★★★★ Very good
Route interest : ★★★★★ Very good
Very busy route : No

Very nice walk,

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Lydmil
Lydmil

Overall rating : 4.7 / 5

Date of your route : Apr 10, 2025
Reliability of the description : ★★★★☆ Good
Ease of following the route : ★★★★★ Very good
Route interest : ★★★★★ Very good
Very busy route : No

We loved this hike for its diversity and interest. Varied landscapes. Great walk. Be sure to check your route using GPS. Avoid the descent from the castle if you are not wearing suitable footwear, as it is steep and slippery (points 14-15)
Your dog will enjoy this walk, which follows the river for a good part of the way.

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Céüse
Céüse

Overall rating : 5 / 5

Date of your route : Nov 10, 2024
Reliability of the description : ★★★★★ Very good
Ease of following the route : ★★★★★ Very good
Route interest : ★★★★★ Very good
Very busy route : No

Very nice walk, very well detailed.
Thanks to the author!

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Pissoulit
Pissoulit

Overall rating : 4.3 / 5

Date of your route : Aug 18, 2024
Reliability of the description : ★★★★☆ Good
Ease of following the route : ★★★★★ Very good
Route interest : ★★★★☆ Good
Very busy route : No

Great hike! Very little traffic in town, mostly through forests or along various fields and meadows (we also walked along part of the Viroin river).

It was perfect for me and my dogs, who were able to enjoy the smells of nature (there were very few people around during our walk).

Be careful between points (12) and (15) as there is a lot of mud, so make sure you wear suitable walking shoes, especially if you are going during the wet season or after heavy rain.

I recommend it

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Carlito1212
Carlito1212

Overall rating : 4.7 / 5

Date of your route : Aug 12, 2024
Reliability of the description : ★★★★★ Very good
Ease of following the route : ★★★★★ Very good
Route interest : ★★★★☆ Good
Very busy route : Yes

A very beautiful hike and a wonderful discovery of a very beautiful region. A little noisy because there are quite a few scout camps in the area. But that doesn't detract from the beauty of the route.

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michel tout court
michel tout court

Overall rating : 5 / 5

Date of your route : Jul 16, 2024
Reliability of the description : ★★★★★ Very good
Ease of following the route : ★★★★★ Very good
Route interest : ★★★★★ Very good
Very busy route : No

A very beautiful hike offering many geological curiosities, information about trees and shrubs, and beautiful views.
Take care in some places in wet weather.
Recommended

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JVS59000
JVS59000

Overall rating : 5 / 5

Date of your route : Apr 13, 2024
Reliability of the description : ★★★★★ Very good
Ease of following the route : ★★★★★ Very good
Route interest : ★★★★★ Very good
Very busy route : No

A superb hike with a very varied route (water, woods, paths). Magnificent geological and historical discoveries, beautiful views.
The route is very well described, with no risk of getting lost.
Well done!

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Aurémosaique
Aurémosaique

Overall rating : 5 / 5

Date of your route : Aug 20, 2022
Reliability of the description : ★★★★★ Very good
Ease of following the route : ★★★★★ Very good
Route interest : ★★★★★ Very good
Very busy route : No

A wonderful discovery

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smashdc
smashdc

Overall rating : 4.7 / 5

Date of your route : Apr 17, 2022
Reliability of the description : ★★★★☆ Good
Ease of following the route : ★★★★★ Very good
Route interest : ★★★★★ Very good
Very busy route : No

Don't hesitate to give it a go. There are lots of interesting things to see on this hike!
Find out more here: https://youtu.be/fVOUvzrl2Ic

The first part of the hike is mainly in the forest with very limited views and a passage through the arboretum. But it's fine.
There are points of interest and some beautiful long straight stretches further on! Very beautiful forest.
No problems with the Visorando app for the route (+ GPS watch): I followed the app and my watch. No issues.
The app is free, so if the descriptions aren't enough (which they always are), use it.

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Emeline.C
Emeline.C

Overall rating : 3.5 / 5

Date of your route : Mar 19, 2022
Reliability of the description : ★★★☆☆ Average
Ease of following the route : Not used / Not applicable
Route interest : ★★★★☆ Good
Very busy route : No

Hello,

As mentioned in numerous comments, the route is extremely unclear after Fondry des chiens. In fact, between points 6) and 9), it was very difficult to find our way...(impossible to follow the description). We wasted a lot of time trying to find a way to continue (even the GR signs were no longer visible) and ended up getting lost... The itinerary should mention if we had to pass any barriers and/or "key landmarks". Due to this lack of clarity, we missed the rock with the hole in it...Similarly, at point 12), we never found the railway track or the "red balustrade"... It's a real shame because overall there were some beautiful points of interest, the landscapes were magnificent and the route was very quiet. Room for improvement, then...

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GCO1
GCO1

Overall rating : 4.7 / 5

Date of your route : Jan 31, 2022
Reliability of the description : ★★★★★ Very good
Ease of following the route : ★★★★☆ Good
Route interest : ★★★★★ Very good
Very busy route : No

xx

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Papou etienne
Papou etienne

Overall rating : 5 / 5

Date of your route : Jan 27, 2022
Reliability of the description : ★★★★★ Very good
Ease of following the route : ★★★★★ Very good
Route interest : ★★★★★ Very good
Very busy route : Yes

Good evening, thank you for this superb hike, a real treat. Despite the light rain, we were able to enjoy the route. Be sure to check the hunting schedule. We'll definitely be back in the spring... Congratulations...

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Pierre Maurissen
Pierre Maurissen

Overall rating : 3.7 / 5

Date of your route : Jun 07, 2021
Reliability of the description : ★★★☆☆ Average
Ease of following the route : ★★★☆☆ Average
Route interest : ★★★★★ Very good
Very busy route : No

The directions are sometimes unclear or imprecise (especially after Fondry des Chiens).
It would have been useful to specify that a large part of the route follows the GR de Pays trail.
Nevertheless, it was a very nice walk, thank you.

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