Ultra-Trail Snowdonia by UTMB®
Ultra-Trail Snowdonia by UTMB® – UTS 100K
Llanberis
Race guide
Updated 18 July 2026
The UTS 100K is the centrepiece hundred at Ultra-Trail Snowdonia by UTMB, a 106 km loop out of Llanberis with 5234 m of positive climbing. That is more than 49 m of ascent for every kilometre, and it earns Ultra-Trail Snowdonia its reputation as one of the steepest, most physical courses on the UTMB World Series calendar. The high point is only 991 m, but on this route altitude is not the story; the sheer density of steep climbing and descending is. The course is built on a distinctive rhythm: the checkpoints sit low, in the valleys and villages of Eryri, while the climbing hides in between. You drop into places like Blaenau Ffestiniog and Beddgelert almost at sea-level heights, then haul yourself back up to ridgelines before plunging into the next valley. Add a chain of firm cut-offs from Gwastadannas Farm through to the Llanberis finish, and the UTS 100K becomes a race of relentless up-and-down that must be respected from the very first climb.
The course: a valley-to-summit loop from Llanberis
The UTS 100K is a 106 km loop starting and finishing in Llanberis at 105 m. Its checkpoints trace a tour of Eryri's valleys: Gwastadannas Farm at 14.1 km (95 m), Dolwyddelan at 29.3 km (143 m), Blaenau Ffestiniog at 41.8 km (223 m), Croesor at 54.1 km (157 m), a return to the Gwastadannas area at 67.5 km (101 m), Beddgelert at 81.6 km (46 m), and Rhyd Ddu at 95.9 km (189 m) before the climb home to Llanberis. Every one of those aid stations sits low. That is the key to reading this course. With a high point of 991 m but checkpoints between roughly 46 and 223 m, the 5234 m of climbing is packed into the sections between aid stations. You are almost never running level: you either grind up toward a ridge or descend hard into the next valley to reach food and water. Plan your day around those valley-to-summit-to-valley cycles rather than around the flat, because there is very little of it.
Where the race is won or lost
The decisive climbs are the big pulls that link the low checkpoints. Because every aid station drops you back toward the valley floor, each leg forces a substantial ascent to reach the high ground near the 991 m top and a steep descent to the next station. The stretches around the deepest valley points, such as the leg into and out of Beddgelert at 81.6 km (46 m), demand fresh legs precisely when you have the fewest kilometres left, and this is where the hundred is often decided. The closing section from Rhyd Ddu at 95.9 km (189 m) back to Llanberis at 106 km (105 m) is the sting in the tail: after more than 95 km and the bulk of the 5234 m behind you, there is still climbing to do before the final drop into town. Runners who spent recklessly on the early descents arrive here with wrecked quads and pay dearly. The winning approach is to climb efficiently by hiking the steep pitches and to descend with control, saving the legs for a course that never truly lets up.
How to pace, crew and fuel it
The cut-offs give the UTS 100K its backbone: Gwastadannas Farm by Sat 10:30, Dolwyddelan by Sat 14:30, Blaenau Ffestiniog by Sat 18:30, Croesor by Sat 22:00, the Gwastadannas return by Sun 02:00, Beddgelert by Sun 06:30, Rhyd Ddu by Sun 11:00, and the Llanberis finish by Sun 14:00. These are spaced to reward steady, sustainable progress; if you find yourself scraping an early barrier such as Gwastadannas Farm, take it as a signal that the course is already outrunning you and adjust before the deficit grows. Crew access is available at Dolwyddelan (29.3 km), Blaenau Ffestiniog (41.8 km) and Beddgelert (81.6 km), so build your plan around those three points for warmer kit, resupply and a morale lift. The longest carries include the roughly 14 km opening leg to Gwastadannas Farm and the leg into Beddgelert, so leave each aid station with enough fluid and calories for a big climb. Eat consistently through the day and night, because 5234 m of climbing burns through reserves quickly and the low valleys offer no easy recovery.
Conditions to expect in Eryri
Although the high point is only 991 m, this is serious mountain terrain in Eryri (Snowdonia), and the weather can turn quickly on the higher ground between the valley checkpoints. Expect a wide range across the loop: sheltered, sometimes warm valleys around Beddgelert (46 m) and Blaenau Ffestiniog (223 m), and colder, windier, more exposed conditions on the climbs toward the 991 m top. The race runs deep into the night before the Sun 14:00 finish, so plan for a full overnight with a reliable headtorch, spare batteries and layers that handle both effort-heat on the climbs and chill on the descents. The ground itself is what makes UTS famous. The steep gradients that generate 5234 m of climbing in 106 km mean rocky, technical, often wet trail that is slow to climb and demanding to descend, especially in the dark and after many hours on your feet. Choose shoes with aggressive grip, keep your footing deliberate on the long descents into the valleys, and treat the whole course with patience: on this loop, consistency and good decision-making beat early speed every time.
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Checkpoints & cut-offs
✓ Course data verified against the official source (2026-07-17) · official source
0 km · 105 m · —
14.1 km · 95 m · Sat 10:30
29.3 km · 143 m · Sat 14:30
41.8 km · 223 m · Sat 18:30
54.1 km · 157 m · Sat 22:00
67.5 km · 101 m · Sun 02:00
81.6 km · 46 m · Sun 06:30
95.9 km · 189 m · Sun 11:00
106 km · 105 m · Sun 14:00
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