Ultra-Trail Snowdonia by UTMB
Ultra-Trail Snowdonia by UTMB (UTS 100M)
Llanberis
Race guide
Updated 29 June 2026
Ultra-Trail Snowdonia by UTMB (UTS 100M) is a 163 km loop starting and finishing in Llanberis, threading through the full breadth of Snowdonia with 8942 m of ascent and a high point of 1065 m on the Snowdon massif. It is one of the most technically demanding UTMB-series races in the UK, crossing boggy moorland, loose quarry spoil, rocky ridgelines and steep valley paths in conditions that can shift from clear to brutal within hours. The route visits 12 aid stations across three days, weaving through iconic Welsh landmarks — Ogwen Valley, Blaenau Ffestiniog, Croesor, Beddgelert and finally Yr Wyddfa (Snowdon summit) — before descending back to Llanberis with a hard cut-off at Day 3 14:00. What makes this race defining is not any single climb but the relentless accumulation: by the time you reach Snowdon at km 132.8 you will have already banked nearly 8000 m of gain, and the mountain demands full respect regardless.
Course & Terrain Overview
The loop begins in Llanberis (105 m) and climbs immediately toward Pen-y-Gwryd Hotel at km 11.9, gaining over 250 m in the opening section before dropping into the Ogwen Valley (Glan Dena, km 21.1, 311 m). From Ogwen the route pushes east toward Llyn Cowlyd and the MCNW Hut at km 37.3 — remote, exposed moorland where navigation demands attention, especially in low visibility. The first major crew point is Capel Curig at km 49.5 (188 m), a genuine psychological waypoint marking the end of the opening mountain block. The middle third — Dolwyddelan (km 60), Blaenau Ffestiniog (km 72.3) and Croesor (km 84.6) — runs through old slate quarry country: loose underfoot, often wet, and deceptively hilly despite lower elevations. Gwastadanas Farm at km 98.2 (75 m) represents the course's lowest point, and from Beddgelert (km 112.2) the terrain turns decisively upward again toward the Snowdon group. Throughout, expect a mix of narrow sheep tracks, open bog, rocky scrambles and the occasional tarmac road link. Gaiters are strongly advised; poles are used by the majority of competitive finishers.
Decisive Climbs and Where the Race Is Won or Lost
The race has two defining blocks of climbing. The first spans km 0–37 (Llanberis to Llyn Cowlyd), where cumulative ascent and technical footing punish anyone who treats the opening hours as a warm-up jog. Many runners overcook this section drawn in by fresh legs and relatively runnable valley paths — the gradient looks manageable on the profile but the ground underfoot adds significant effort. The second, and race-defining, block is the approach to Yr Wyddfa (Snowdon summit, ~1085 m, km 132.8) from Rhyd Ddu Outdoor Centre (km 126.9, 225 m): roughly 800 m of vertical gain over 5.9 km at well past the 130 km mark. By this point your legs have absorbed more than 7500 m of prior climbing. The descent from Snowdon summit back toward Bron y Fedw Uchaf Farm (km 139.1, 151 m) is steep and technical, requiring working quads and attentive footwork in the dark or in poor weather — this descent alone has ended many otherwise strong races. The final stretch from Betws Garmon (km 147.4) to Llanberis (km 163) contains more undulation than runners expect this late in the game, and the cut-off at Day 3 14:00 has teeth.
Pacing & Racing Strategy
The evidence from runners who have done this well is unambiguous: a patient, almost social first half is the deposit that funds a strong second. The valley sections between Llanberis and Capel Curig feel generous and inviting — that is precisely the trap. Going through Capel Curig (km 49.5) feeling controlled and slightly under-cooked is the goal, not a warning sign. The real race begins on the far side of the first night, and whatever you spend before dawn is borrowed against your Snowdon ascent. From Beddgelert onward, you are entitled to push: break the remaining distance into manageable chunks ('two more aid stations and I'm home') and manage each segment as its own problem rather than staring at the total. The record-breaking approach in this kind of event consistently comes from going easy early, not hard — trust that the fitness is there and let the later kilometres reveal it. Use the crew points at Capel Curig (km 49.5), Dolwyddelan (km 60), Blaenau Ffestiniog (km 72.3), Croesor (km 84.6), Beddgelert (km 112.2) and Rhyd Ddu (km 126.9) to execute planned resets: change socks, eat real food, reset your mental frame. Do not skip these opportunities in pursuit of time — the investment pays compound returns.
Fuelling Across 163 km
With aid stations roughly every 10–15 km through the middle section and crew access at six points, there is no excuse for arriving at Snowdon depleted — but it happens constantly. Prioritise eating at every stop from km 37 onward, regardless of appetite. The section from Gwastadanas Farm (km 98.2) to Beddgelert (km 112.2) — 14 km with significant climbing — is a common low point where blood sugar crashes compound accumulated fatigue; top up aggressively at km 98.2. Carry at least 500–750 ml of fluid capacity between stops given the exposed moorland sections where streams may not be reliably potable. Caffeine management matters on a potential 60–80+ hour race: save meaningful doses for the second night and the Snowdon climb rather than burning through your caffeine sensitivity in the first 12 hours. Solid food tolerance tends to drop sharply after km 100 — practice eating by effort not by hunger in training, and keep a selection of textures in your pack for the sections when gels alone become repellent.
Conditions to Expect
Snowdonia is one of the wettest mountain environments in Wales, and the UTS 100M route crosses some of its most exposed terrain. Even in summer race conditions, temperature on Yr Wyddfa summit (km 132.8, ~1085 m) can be 10–15°C colder than the valley with significant wind chill; a full waterproof shell, insulation layer and gloves must be carried and accessible, not buried at the bottom of your pack. Ground conditions across the moorland sections — particularly around Llyn Cowlyd (km 37.3) and the Croesor–Gwastadanas stretch (km 84–98) — are reliably boggy regardless of recent weather. The quarry terrain around Blaenau Ffestiniog (km 72.3) can be slippery on wet slate. Expect at least one full night section and plan your headtorch battery capacity accordingly — most mid-pack runners will experience two nights out. Sunrise on the Snowdon ridge after a hard second night is among the more memorable moments this race offers, but earn it with proper kit and realistic pacing rather than heroics in the first valley.
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Checkpoints & cut-offs
✓ Course data verified against the official source (2026-07-05) · official source
0 km · 105 m · —
11.9 km · 372 m · Fri 17:30
21.9 km · 305 m · Fri 20:00
37.2 km · 373 m · Sat 00:30
49.5 km · 192 m · Sat 03:00
59.8 km · 143 m · Sat 06:00
72.3 km · 223 m · Sat 09:30
84.6 km · 164 m · Sat 13:00
98.2 km · 89 m · Sat 16:45
112.3 km · 46 m · Sat 20:30
126.7 km · 186 m · Sun 02:00
139.2 km · 152 m · Sun 06:45
147.5 km · 128 m · Sun 09:45
163.9 km · 105 m · Sun 14:00
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