GR 20 (Corsica)

The hardest stretch on the trail, and it is hard from the first hour. An old mule track climbs out of Calenzana through maquis and forest, but the scrub gives out around Bocca a u Saltu at about 1,250 m and everything above that is granite: slabs with chains bolted to them, boulder crests where hands are in constant use, and descents on unstable, slippery rock that cost as much time as the climbs. The Spasimata footbridge and the smooth canted slabs above it carry more cable than the rest of the route put together, and they are the most exposed ground a walker meets here. It closes with the biggest single climb the GR20 offers, roughly 1,200 m out of Ascu Stagnu onto the Monte Cinto ridge at just under 2,600 m, which is the line that replaced the Cirque de la Solitude in 2016. Three quarters of the first day is in the open, and above the tree line there is no shade at all.

Logistics: No departure on the GR20 from Calenzana is authorised after 11:00. That is the park's own wording, on its own GR20 page, and a Corsican GR20 safety guide repeats it in the same terms; it is a fire-risk measure rather than a suggestion. This first stage is roughly 1,400 m of climb to Ortu di u Piobbu, so the rule kills the itinerary most people arrive with: land at Calvi in the morning, take the bus up, start walking. Sleep at Calenzana and leave at first light instead. The Cirque de la Solitude is not an alternative. Its chains and ladders were removed, it is no longer waymarked and the park does not treat it as a variant, but older guidebooks and downloaded tracks still route through it from Ascu Stagnu.

Navigation: Red and white flashes the whole way, but paint on bare granite is easy to miss on the boulder crests where you are watching your feet rather than the skyline. The real navigation question on this stretch is not the marks but the tracks people carry: the Cirque de la Solitude line out of Ascu Stagnu is unmarked and abandoned, and the current route climbs toward Monte Cinto instead.

Seven kilometres that are almost entirely downhill and none of it casual. From the high point the line loses height along the crest, past Lac du Cinto, to Bocca Crucetta at 2,456 m, and then falls about 800 m in two and a half kilometres, steep scree at first and then a cairned path down to Tighjettu. Knees do this one, not lungs. Below the huts the ground changes completely: the valley floor at Ballone, then the Albertacce forest with the young Golo beside it and pools worth stopping at, and after the Cinto crossing that transition from mineral to shade and running water is the reason a lot of people stop early here rather than push on.

Logistics: There is one thread of GR20 through here and nothing beside it. This trail's stored geometry is a single unbroken section from Calenzana to Conca, so anything that shuts the ground between Tighjettu and the bergeries of Ballone breaks the route rather than diverting it, and the way out is on foot down the valley to Calasima and Albertacce. That matters more here than elsewhere because this is fire country from midsummer. Closures on this ground are made by prefectoral order rather than by advice, they apply in both directions, they run until further notice, and the GR20 between Tighjettu and Ballone has been closed that way. Check the daily Corsican fire-risk map, reissued each evening at about 18:00, and the Haute-Corse prefecture's forest-massif access page before you leave home and again before you walk this stage. A track you downloaded in winter is not evidence that the ground is open.

Navigation: Cairned all the way down and unproblematic once the scree is behind you. The forest and valley section is an ordinary waymarked path.

The long middle of the northern half, and the only part of the north that gives something back. It opens with a steep 500 m pull past the Brèche du Sphinx to Bocca di Foggiale under Paglia Orba, then follows the Golo down past the Radule waterfall to Col de Vergio, the one road on the 45 km between Ascu Stagnu and Vizzavona. What follows is the gentlest walking on the GR20: forest track to the col at San Pedru and then Lac de Nino, a shallow lake ringed by pozzines, peat lawns pocked with water holes and grazed by loose horses, cattle and pigs, wet underfoot and unlike anything else on the route. It hardens again at Manganu, where 600 m of scree and fixed ladders lift you into the Brèche de Capitello and the trail becomes a high rock traverse above the Restonica lakes, over Bocca a Rinoso and Punta Muzzella, that stays above 2,000 m for hours. From Petra Piana the main line drops into the Manganellu valley, wooded, cool and full of pools, before climbing back to l'Onda and over Bocca Muratella. Two entirely different trails inside one section.

Logistics: From Petra Piana the route divides: the main GR20 takes the Manganellu valley past the Bergeries de Tolla, which is longer and easier, while a marked ridge variant runs high over Bocca d'Oreccia and Pointe de Pinzi Corbini. They rejoin at l'Onda, and the variant is the one to leave alone in poor weather.

Navigation: Waymarked throughout and mostly obvious, but this is the section with alternatives, and that is where people go wrong rather than at the paint. From Petra Piana the main GR20 and the ridge variant both look like the trail and diverge for eight kilometres. Downloaded tracks do not always match the line under your feet, which is worth knowing before you are standing on a col deciding.

The section where the trail changes. It starts on the far side of Bocca Muratella with the steepest descent on the GR20, about 1,100 m down the Agnone valley past the Cascades des Anglais into Vizzavona, rocky and hard on knees. Vizzavona is the midpoint, the only station on the route, and the classic place to cut the walk in half. South of it the ground softens: laricio pine and beech, broad forest paths and old shepherds' tracks, cols at 1,600 m instead of 2,200, and shade for most of the day. From Bocca Palmente the route runs out onto open pasture and bergeries below Monte Renoso to Capanelle, then across the Gialgone plateau and down through the Marmano beech forest to Bocca di Verdi at 1,289 m, the lowest ground since Vizzavona. The climbing does not stop, but the hands stay out of it.

Logistics: Vizzavona is where the GR20 divides into its northern and southern halves, and a large share of walkers start or finish here rather than walking through. Everything south of it is a different order of difficulty from everything north.

Navigation: Easier ground but more junctions than the north. The climb out of Vizzavona toward the Bergerie de Cimoni crosses several paths and needs the marks watched rather than assumed, and further south the route shares ground with forestry tracks. Cloud matters much less here because most of the day is under trees.

The southern crest, and the finest long ridge walking on the trail. The section begins partway up the beech-forest climb out of Bocca di Verdi and reaches the watershed at Prati, where the ground opens and stays open: for the next couple of hours the path runs along the crest itself, crossing from the east flank to the west and back, with the coastal lagoons and, on a clear day, Elba on one side and the interior on the other. It skirts the base of Punta della Cappella, drops to the beech at Bocca di Laparo, climbs again around Monte Formicula, and then comes the Arête a Monda, roughly three kilometres of rock crest beyond Usciolu where the line threads between granite blocks and progress is slow whatever your fitness. The trail then falls off the ridge through beech at Bocca di l'Agnone and out onto the Plateau du Coscione, a broad grazed upland of pozzines, shallow lakes and standing water that is the easiest walking in the southern half, before tilting up again onto the shoulder of Monte Incudine. Exposed for most of its length, with nothing quick to drop down to.

Logistics: From Usciolu a marked alpine variant runs direct to Asinau and misses out the Coscione plateau, turning sixteen stages into fifteen. The plateau is the main GR20 and the lower, kinder option in bad weather.

Navigation: Two different problems. On the crest between Prati and Usciolu the path keeps changing sides of the ridge, so the marks matter more than the skyline and in cloud it is easy to follow the obvious crest and lose the route. On the Arête a Monda the line threads between blocks and needs picking out at close range. The Plateau du Coscione is the reverse case, open grazing with no natural line to follow.

Downhill on paper and much longer in the legs than that suggests. It begins on the crest of Monte Incudine, which the trail crosses at just over 2,000 m below the 2,134 m summit, the last high ground of the walk, and drops steeply to Asinau. From there the main line contours the west side of the Bavella massif on a shaded, well-made forest path, while the marked alpine variant climbs into the Aiguilles themselves, a chained and genuinely aerial scramble that is the hardest optional ground on the route and lands on the second-to-last day when legs are gone. Both finish at the Col de Bavella. Beyond Paliri the mountain ends: granite gives way to sandy paths, the maquis grows taller and greener the lower you go, and the final stretch keeps producing another small climb every time it looks finished, including one after the 587 m Bocca d'Usciolu that is traditionally called the door of the GR20. Hot, open and unshaded on that last ground. The section reads as populated only because three dozen mapped hamlet names cluster around Conca at the finish; the route passes nothing until the village itself.

Logistics: The alpine variant over the Aiguilles de Bavella and the low forest route are both marked and both end at the col. The variant is a via-ferrata-like scramble on chains for experienced walkers in settled weather; the forest path is the all-weather line and is not a lesser route, just an easier one.

Navigation: The junction after Asinau, where the alpine variant leaves the main GR20, is the one to get right, because the two routes are not remotely equivalent and the decision is easier made at the sign than halfway up. From Bavella onward the marking is straightforward.