Ultra-Trail Snowdonia by UTMB®
Ultra-Trail Snowdonia by UTMB® – ERYRI 25K (NEW ROUTE)
Llanberis
Race guide
Updated 18 July 2026
The ERYRI 25K is the short-course option at Ultra-Trail Snowdonia by UTMB, run on a new route as a loop from Llanberis in the heart of Eryri (Snowdonia). It covers 22 km with 1090 m of positive climbing and a high point of 723 m, a ratio that tells you almost everything you need to know: this is a small distance with a big vertical bite. Do not be misled by the modest kilometre count. At close to 50 m of climb for every kilometre on average, the ERYRI 25K packs the kind of relentless up-and-down that defines Ultra-Trail Snowdonia, compressed into a single loop that starts and finishes at Llanberis (105 m). It is a hard, honest mountain race for runners who want a true taste of Eryri terrain without committing to the longer UTS distances.
The course: a steep loop from Llanberis
The ERYRI 25K starts and finishes in Llanberis at 105 m, making a 22 km loop back to the same point. Over that loop it climbs 1090 m and reaches a high point of 723 m, so the route lifts you well over 600 m above the start before returning you to it. With the start and finish at identical altitude, every metre climbed has to be given back, and the descending is as much a feature of this course as the ascending. Because this is the new route and the published course data marks only the start and finish, the exact placement of the climbs is best confirmed on the official course profile and race briefing. What the numbers make clear is the shape of the day: a compact loop with a lot of vertical relative to its length, so plan for sustained climbing and steep, sometimes technical descending rather than long runnable flats.
Where the effort concentrates
With 1090 m of climb in 22 km, the ERYRI 25K averages roughly 50 m of ascent per kilometre. In Eryri that rarely arrives as one smooth gradient; it comes as sharp pitches that force you to hike, interspersed with ground steep enough downhill to punish the legs. The high point of 723 m is the pivot of the race, and how you arrive there and how you handle the drop back toward Llanberis will shape your finish time far more than raw speed on any flat section. Because the loop returns to its 105 m start, the closing kilometres involve losing height back to the valley. On a course this steep that descent is where quads fatigue and footing matters most. Runners who climb within themselves and stay light and controlled on the downs will finish strong; those who force the climbs risk arriving at the descents with nothing left to brake and balance.
How to pace and manage the cut-off
The ERYRI 25K carries a single cut-off, at the finish in Llanberis at Sun 14:00. That gives most runners a workable window, but the vertical profile means your moving pace will be far slower than a flat 22 km would suggest, so do not bank on road-race splits. Budget generous time for the climbs, where hiking is often faster and more efficient than trying to run, and treat the descents as your chance to make up ground. Because the intermediate support and checkpoint detail for the new route should be taken from the official briefing, plan your own fluid and food to be self-sufficient across the loop. Carry enough to climb 1090 m and cover 22 km of mountain terrain comfortably, eat early and steadily rather than waiting until you are depleted, and keep a simple rule in mind: protect your legs on the way up so they still work on the way down.
Conditions to expect in Eryri
This is a mountain loop in Eryri (Snowdonia) topping out at 723 m, and mountain weather here can change quickly regardless of the forecast in the valley. Expect the conditions at the 723 m high point to differ from Llanberis at 105 m, with more wind and exposure the higher you climb. Carry and wear layers you can adjust, and be ready for the ground and visibility to feel more serious up high than they do at the start line. The terrain that produces 1090 m of climbing in just 22 km is, by definition, steep, and in Eryri that usually means rocky, uneven, and sometimes greasy underfoot. Choose shoes with dependable grip, keep your concentration on the technical descending back toward Llanberis, and respect the Sun 14:00 cut-off by keeping your stops brief. A compact course like this rewards steady forward motion over bursts of speed.
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