How difficult is the 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.

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.

In poor weather: Rain is what matters here rather than wind. The Spasimata slabs are smooth, convex and tilted above a gorge, and wet they become a skating rink, which is exactly what the cables are for; the loose descents off Punta Innominata and Bocca di Stagnu get slower and more treacherous in the same conditions. Heat is the other half of it, because most of the first day and everything above the tree line is unshaded.

Escape options: From the first two huts the realistic exit is on foot down the Bonifatu cirque to the Maison Forestière on the D251, from where a taxi reaches Calvi or Calenzana. After that the only road is at Ascu Stagnu at the head of a dead-end valley, which is where most people who give up on the north give up. From Ascu Stagnu onward there is nothing at all, and continuing means the 1,200 m climb to the Cinto ridge.

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.

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

In poor weather: The scree below Bocca Crucetta is the piece that changes: loose and greasy wet, on ground steep enough that a slip runs. In cloud the top of the descent is featureless and becomes a cairn-to-cairn job. The valley below Ballone is sheltered and barely affected by anything.

Escape options: On foot only. The valley below Ballone leads out to Calasima, Albertacce and Calacuccia, and the standard escape list also gives a line off the Cinto descent to the Refuge de l'Erco and Lozzi. Neither is quick, and no road touches the section itself.

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.

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.

In poor weather: The Brèche de Capitello is the weather-critical piece: a scree climb into a notch with ladders and chains as the only way through, and no way round. The traverse beyond it runs on open rock above 2,000 m for a couple of hours with nothing to shelter behind on either side. The Col de Vergio to Lac de Nino stretch and the Manganellu valley are the opposite, forest and pasture that stay perfectly walkable in weather that would stop the ridge, which makes them the sensible ground to be on when a storm builds.

Escape options: Col de Vergio is the good one, a road pass with the hotel and shop at the col itself and a bus down to Corte. Otherwise the exits are long walks: from the Brèche de Capitello a path drops east past the Capitello and Melo lakes to the Bergeries de Grotelle at the head of the Restonica road above Corte, and from the Manganellu valley at the Passerelle de Tolla a path leads out to Canaglia and Tattone in under an hour, which is the easiest exit anywhere in the second half of the section.

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.

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.

In poor weather: The Agnone descent into Vizzavona is rock and root beside a stream and is genuinely slippery wet, which is the one place on this section where rain costs real time. Everything south of Vizzavona is sheltered forest, tolerable in wind and rain; the weather that actually bites here is heat on the open pasture between Bocca Palmente and Capanelle, where the shade stops.

Escape options: The best on the trail. Vizzavona has the station and a village around it, and stopping there is a plan rather than a retreat. Capanelle has a road down the D169 to the D69 near Ghisoni, and Bocca di Verdi sits on the D69 itself between Ghisoni and Cozzano, but neither col has a scheduled service, so treat both as places you can be collected from rather than places you can leave under your own steam.

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.

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.

In poor weather: The most exposed sustained stretch south of Vizzavona. Between Prati and Usciolu you are on or just below the crest for hours with no shelter and no quick descent either side, and this is the ground where an afternoon storm is a genuine problem rather than an inconvenience. Wet granite on the Arête a Monda slows a stretch that is already slow. The Coscione plateau is the exception, low and sheltered, though it is wet ground and stays wet.

Escape options: Both real exits are on foot and both head west off the crest. From Bocca di Laparo a Mare a Mare path drops to Cozzano; from Usciolu the descent leads to Cozzano or Zicavo. Both villages sit on the road toward Ajaccio and an exit here means a night in the village. Between Bocca di Verdi and the plateau there is no road at all.

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.

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.

In poor weather: Heat is what this section deals in, not rain. Below Paliri the trail loses 800 m into maquis and sand with almost no shade, which is why an early start off Paliri is worth more here than anywhere else in the south. The alpine variant is the opposite case, chained rock at altitude that should be left alone in wind, cloud or a building storm, with the low forest path as the answer on those days.

Escape options: Col de Bavella is the last road, on the D268 with Zonza to the south and Solenzara on the coast to the north, and it is a genuine place to stop rather than a retreat. After it there is nothing: Paliri is reached on foot only and no road touches the final thirteen kilometres into Conca.