GR 20

The GR 20 runs the length of Corsica's mountainous spine — 180 km from the Balagne village of Calenzana, near Calvi in the north, to the Mediterranean hamlet of Conca above the Gulf of Porto-Vecchio in the south. It crosses the watershed of the island, weaving between summits in the 2,000–2,700 m range and stitching together a chain of refuges built and maintained by the Parc Naturel Régional de Corse. Long held to be the toughest of France's grandes randonnées and routinely called the hardest waymarked long-distance trail in Europe, it climbs a cumulative 12,000 m across roughly 15 days of refuge-to-refuge walking.

The trail divides naturally at Vizzavona, the small rail-served hamlet at the halfway point. The northern half is the brutal half: jagged red granite, scrambly traverses on slabs above big drops, the via-ferrata-like climb out of Carrozzu, the Cirque de la Solitude bypass through Pointe des Éboulis, and Monte Cinto's 2,706 m looming over everything. Days are short in distance but long in time — eight kilometres can take eight hours. South of Vizzavona the character softens into laricio-pine forest, the rolling Coscione plateau, and the long ridge of Monte Incudine before the trail tips off Bavella's spires down to the sea. The waymark — a red and white stripe — is unrelenting; route-finding is rarely the problem, but Corsica's afternoon thunderstorms and the exposed ridges above Asco and Cinto are.

The walking window runs mid-June to mid-September, when the PNRC refuges are staffed and the high passes are reliably free of snow. Booking is mandatory and competitive in July and August — reservations open in spring on pnr-resa.corsica and the popular refuges (Ortu, Carrozzu, Tighjettu, Manganu, Petra Piana) fill within hours. Each refuge offers dormitory beds, pre-pitched canvas tents, and bare camping pitches at decreasing prices; meals are bookable separately. There is no resupply between huts beyond what the wardens stock, and water is plentiful but should be filtered. Most hikers walk north to south to get the hardest sections done while fresh; trail runners and the very fit do the whole thing in a week, the record under 32 hours.