Monts d'Arrée: Roc'h Trévezel Ridge Walk

The Monts d'Arrée in Finistère form the ancient geological backbone of Brittany, a ridge of quartzite and schist remnants from the Hercynian orogeny that constitute the highest ground in the region. The Roc'h Trévezel circuit begins at the Col de Roc'h Trévezel lay-by on the D785 road near Brennilis and completes a 12-kilometre loop crossing open moorland, boggy valleys, and the summit quartzite ridge at 364 metres — the third-highest point in Brittany.

The approach from the col follows a clear waymarked track onto open heathland, initially through gorse and broom before transitioning to blanket bog habitat dominated by bog cotton, sundews, and cross-leaved heath. This is one of the last significant areas of upland blanket bog in Brittany and is protected within the Parc Naturel Régional d'Armorique. Walkers must remain on marked paths to avoid damaging the fragile peat surface, which can be deceptively deep away from the trail.

The ridge section involves short quartzite rock scrambles requiring use of hands in places — nothing technical, but sturdy boots with grip are essential. The summit trig point rewards with a panoramic view across the Monts d'Arrée, the Lac du Drennec reservoir to the south (which flooded the former village of Brennilis in the 1970s), and on clear days as far as the Bay of Biscay. The Roc'h Ruz transmitter tower is visible to the west. Local legend places the entrance to the Celtic underworld (Youdig) at the Yeun Elez bog below the ridge.

The descent returns through valley woodland before crossing the D785 back to the col car park. Total ascent is approximately 380 metres. No water sources exist on the route and no refuge huts are present; carry a minimum of one litre from departure. The trailhead is car-only — no public transport serves Brennilis — accessed from Carhaix-Plouguer (30 km) or Morlaix (50 km).