The Ardennes are the reason Benelux trail running is not a contradiction in terms. Across Wallonia, Luxembourg and into the German Eifel, the plateau is cut by the Ourthe, the Semois, the Amblève and the Vesdre into steep wooded valleys, and the result is terrain that behaves like a mountain range even though nothing in it reaches 700 metres. The climbs are short and relentless rather than long and graded, the descents are rocky and wet, and the vertical gain adds up faster than the map suggests.
If you run in the Netherlands, this is where you go to find out what your legs can actually do. Here are the races in our calendar worth building a season around.
Ultra Trail Haute Ardenne: the line across the roof of Belgium
The best concept in Benelux trail running. The Ultra Trail Haute Ardenne draws a line between the country's two highest points: it starts at Waimes below the Signal de Botrange at 694 m, crosses the high moorland of the Hautes Fagnes, and finishes 100 km and some 3,300 m of climbing later at the Baraque de Fraiture, the second summit at 652 m. Point-to-point in the truest sense, with no loops and no repeats.
The shorter Saturday races are entry points onto the same line — 75 km from Malmedy, 60 from Stavelot, 42 and 28 from Trois-Ponts — all converging on the same finish, which makes it unusually easy to pick a distance that suits your year without changing the character of the day. Sunday adds loop courses around Vielsalm and Lierneux on more technical singletrack, and the two days can be combined.
The field stays small: 73 runners finished the 100 km in 2025. Races are ITRA-certified and carry a UTMB Index. The Hautes Fagnes plateau is the one section to respect — it is open moorland, exposed to weather, and quite unlike the sheltered valleys that follow.
Trail des Fantômes: the steepest corner
La Roche-en-Ardenne sits where the Ourthe has cut a deep wooded valley below a ruined medieval castle, and it is about as close to mountain terrain as Belgium gets. The Trail des Fantômes, held on the second weekend of August, is the oldest event on the trailrun.be calendar, run since 2010, and its own organisers rank it among their hardest — which means something in a region where every race climbs.
Expect the classic local recipe: repeated sharp climbs, technical rocky descents and almost no flat on which to recover. The 2026 edition is listed at up to 75 km. If you want a single race to find out whether you can handle Ardennes terrain, this is a strong and brutal candidate.
La Roche also hosts two shorter races that make good reconnaissance for it: the Trail de la Soupe in late November and the Trail des Sangliers in March, both around 57 km on the same kind of ground in very different weather.
Bouillon and the Semois: the best views in the Benelux
Bouillon's fortress rides a rocky spur inside a hairpin bend of the Semois, and the valley walls around it hold some of the steepest and most photogenic trail in Belgium. Two races use it, at opposite ends of the year.
The Trail Godefroy Bouillon in June runs distances up to 100 km through the Semois meanders, and is one of the most in-demand events on the Belgian calendar — recent editions have sold out completely, so entry day matters. The pattern is sharp climbs to ridgeline viewpoints followed by plunging wooded descents, repeatedly.
The Castle Trail Bouillon covers the same terrain in February at up to 50 km, which is an entirely different proposition: frozen mud if you are lucky and the regular kind if you are not, with the castle views intact either way. For a first taste of winter trail racing on real terrain, it is well judged.
Chouffe Trail: the one with the brewery
The Chouffe Trail at Houffalize is a summer weekend built around the Achouffe brewery, with everything from 8 km loops up to a flagship ultra of around 56 km carrying roughly 1,758 m of climbing. The longer routes run fast and technical along the Ourthe valley, with a stop at the brewery itself partway round.
It is the most sociable event on this list and a good introduction to Ardennes climbing: enough vertical to be a genuine test, on a course designed to be enjoyed rather than survived. Past editions have stretched as far as 68 km, so check the current distance menu.
Olne-Spa-Olne: the thirty-year fixture
Olne Spa Olne is the grand old man of Belgian ultras, reaching its thirtieth edition in November 2026: 71 km with 2,296 m of climbing through the Liège Ardennes, starting at eight in the morning with refuelling stations roughly every 16 km.
It trades the short flashy formats of newer events for a long, honest test through the hills between Olne and Spa, in a month when the Ardennes are wet and the days are short. A race for people who like their ultras unglamorous.
Ternellbach: the border ultra
The Ternellbach UltraTrailMarathon starts from the Ternell nature centre near Eupen and covers 45 km through the forests of the Hautes Fagnes-Eifel Nature Park, right on the Belgian-German border. It sits on the German ultramarathon calendar, and it gives runners around Liège and Aachen a genuine 45 km ultra on home ground rather than a repackaged marathon.
Shorter than most on this list, and a sensible first Ardennes ultra if 70 km feels like too large a step.
Legends Trail: the one at the end of the scale
For completeness, and because it is the most serious race in the region: the Legends Trail is 350 km non-stop through the Ardennes in the last week of February, on a route that changes every year, with a rolling cut-off of 4 km/h. That is roughly three and a half days of continuous forward motion through cold, rain, wind, snow and legendary quantities of mud.
At the first edition, 47 runners started and 15 finished. It is not a race you work up to casually, and it is included here so you know where the ceiling is.
What Ardennes terrain actually demands
Four things, and none of them are aerobic fitness.
Climbing strength, in repeated short doses. Ardennes climbs are typically 80 to 200 metres, steep, and come one after another. You do not settle into a rhythm the way you would on an alpine ascent; you do the same hard effort twenty times. Hill repeats are the specific preparation, and power hiking is not optional.
Descending legs. The descents are where Ardennes races are won and where unprepared runners are broken. Eccentric quad loading on steep rocky ground is a trainable adaptation and nothing else substitutes for it. If you arrive with untrained descending legs, you will be walking down by halfway.
Technical footing, often wet. Slate, roots, wet leaves and mud. Grip matters more than cushioning, and in autumn the wet-leaf-over-rock combination is the slipperiest surface of the year.
Weather respect. The Hautes Fagnes plateau and the open ridges are genuinely exposed, and valley weather tells you little about conditions 400 metres higher. This is why Ardennes races enforce mandatory kit more seriously than Dutch ones.
Training for it from the lowlands
If you live in the Netherlands, you cannot replicate this at home, but you can get a long way:
- Find the steepest thing you have and repeat it. A dune, a dyke, a motorway bridge, a car park ramp. Volume of vertical beats gradient authenticity.
- Use stairs for descending. Controlled downhill repeats on steps load the quads eccentrically in a way flat running never does.
- Train in soft sand. Coastal dunes build exactly the calf and ankle strength that rocky ground demands.
- Go south once a month. The Limburg hills are a genuine intermediate step, and the Ardennes themselves are within a few hours of most of the Benelux. Two or three long runs on the real terrain before your race is worth more than any amount of substitution.
Our comparison of the Veluwe and the Ardennes goes into how differently the two regions run, and the full Belgian calendar lists everything above alongside the flatter Flemish races.
Choosing your first one
A reasonable ladder: start with Ternellbach at 45 km or a shorter distance at the Chouffe Trail to learn the terrain. Move to the Trail de la Soupe or Trail des Sangliers at around 57 km, or Olne-Spa-Olne at 71. Then the Trail des Fantômes or the 100 km of the Ultra Trail Haute Ardenne when you want the region's serious tests.
One practical note that applies to all of them: distances, profiles and start times change between editions, and several of these races sell out. Every race page here links straight to the organiser, and that page is always the authority — confirm the date and distance there before you book anything.