huckepack

GR 20

Fra li monti

Length

About 180 km: the stated length (Wikipedia (en)).

Measured on our map line: 183.3 km, the route as OpenStreetMap maps it along the official track. The charts on this page run along the same line, and the search sorts trails by it, so lengths compare the same way.

about180km

Ascent · descent

Estimated from the terrain model, as the sum of every main stage's climbs and drops between samples 100 m apart. No source states them. The model measures the treetops in forests, so it reads high there.

estimated: 12,420m ↑12,430m ↓

Difficulty

How hard a trail is, in three ways: the terrain, the climate in season and the length of the days. Each is rated from Easy to Hard with the same thresholds for every trail, and takes its hardest measure. It describes the trail, not how it will feel to you: that depends on your fitness, experience, pack and the weather you get.

  • Terrain: HardPath grade: ≈ T4
  • Climate: Demanding in Jun–OctHeat: 30 °C by day (July)
  • Effort: DemandingLongest day: 8 h (stage 4)

All measures

Terrain: Hard; Climate: Demanding in Jun–Oct; Effort: Demanding
Suggested
16days

Per stage

The 16 main stages' totals over their number (huckepack), so the averages come from one source. The ascent is the terrain model's estimate per stage (≈), since the stages state no climbs.

11.5km· about 780 m ↑
Season

Landscape

Land cover along the main route, from ESA WorldCover satellite data:

  • Grassland and shrubs: 58%
  • Forest: 39%
  • Bare rock and sand: 3%
  • Farmland and villages: 1%

Landscape along the route

Mostly Grassland

Location

Country
France
Regions
Corsica
Start
Calenzana
Finish
Conca
Route type
Point to point
Travel hubs
  • Gare de Calvi13.1 km by road · 15 min
  • Calvi Sainte-Catherine Airport (CLY)18.1 km by road · 35 min
  • Bastia Poretta Airport (BIA)99.4 km by road · 104 min
Protected areas
Parc naturel régional de Corse
Managed by
Parc naturel régional de CorseOfficial website
Waymarking
Clearly waymarked throughout with white and red marks
  • Trail
  • Start
  • Stage start
  • Finish
  • Contour lines

Difficulty

Terrain

How hard is the ground to walk: the path, the climbing, the steep bits, the ground underfoot? Rated over the whole main route. The rating takes its hardest measure.

Path grade: the trail's SAC grade, stated, converted or estimated.

  1. EasyT1
  2. ModerateT2
  3. DemandingT3
  4. HardT4 to T6

Climbing: ascent of the main stages over their length.

  1. Easyunder 15 m per km
  2. Moderate15–30 m
  3. Demanding30–50 m
  4. Hard50 m or more

Steep stretches: share of the route steeper than 15 %, up or down (terrain model).

  1. Easyunder 5 %
  2. Moderate5–15 %
  3. Demanding15–30 %
  4. Hard30 % or more

Natural ground: share on footpaths and trails (OpenStreetMap); never Hard on its own.

  1. Easyunder a third
  2. Moderatea third to two thirds
  3. Demandingtwo thirds or more

Hard

  • SAC hiking scale

    Trails rate their difficulty in many local scales, or only describe it in words. We translate each rating into the Swiss Alpine Club's hiking scale, from T1 (easy) to T6 (very hard), so trails can be compared. It stays an estimate: how hard a trail feels depends on your fitness, experience, pack and the weather.

    This trail: T4 (our estimate). The park publishes no grade. Its stage texts describe an "increasingly rugged trail that may require the use of hands" from the first day, scree and rockfalls, "technical and very mineral" stages and steep corridors to passes above 2,000 m; English Wikipedia calls it "the most difficult of all the GR routes". Hands needed in places on exposed rock is alpine hiking (T4); the southern half, from Vizzavona, is easier.

    1. T1 · HikingWell-made paths, mostly flat or gently sloping. No risk of falling; trainers are enough.
    2. T2 · Mountain hikingA continuous path, steep in places, where a fall can't be ruled out. Be sure-footed; wear hiking boots.
    3. T3 · Demanding mountain hikingThe path is not always visible; exposed spots may have chains or ropes, and you may need your hands for balance.
    4. T4 · Alpine hikingOften no path. Hands are needed in places, terrain is exposed, and there can be easy snowfields.
    5. T5 · Demanding alpine hikingMostly pathless, with easy climbing and exposed, demanding terrain. Needs alpine experience.
    6. T6 · Difficult alpine hikingPathless, very exposed, with climbing and glaciers. For experienced mountaineers only.

    The scale at the Swiss Alpine Club

    estimated T4
  • Climbingestimated 68 m per km
  • Steep stretches35 % of the way
  • Natural ground96 %

Climate

How hot, cold, wet and windy does it get? Rated for each month from 30 years of weather (ERA5). Without months picked (the search's When filter), the rating is for the trail's best run of at least two months in its season, and each measure shows its hardest month of that run; a pick re-rates it for your months. The rating takes its hardest measure.

Heat: mean daily high at the lowest point.

  1. Easyunder 22 °C
  2. Moderate22–27 °C
  3. Demanding27–32 °C
  4. Hard32 °C or more

Cold: mean nightly low at the highest point.

  1. Easy8 °C or more
  2. Moderate3–8 °C
  3. Demanding−2 to 3 °C
  4. Hardbelow −2 °C

Wet days: days a month with 1 mm of rain or more, the wetter of both points.

  1. Easyunder 10
  2. Moderate10–14
  3. Demanding14–18
  4. Hard18 or more

Snow: days a month with 1 cm of snow or more at the highest point.

  1. Easyunder 1 day
  2. Moderate1–3 days
  3. Demanding3–6 days
  4. Hard6 days or more

Wind: mean of the day's strongest wind (hourly mean, 10 m above ground), the windier of both points.

  1. Easyunder 15 km/h
  2. Moderate15–20 km/h
  3. Demanding20–25 km/h
  4. Hard25 km/h or more

Demanding in Jun–Oct

  • Heat · July30 °C by day
  • Cold · October1 °C at night
  • Wet days · October10 days
  • Snow · October3 days
  • Wind · September12 km/h

Effort

How long are the days? Rated by the longest main stage; a time range counts its upper end. The rating takes its hardest measure.

Longest day: walking time of the longest main stage, stated or by DIN 33466.

  1. Easyup to 4 h
  2. Moderate4–6 h
  3. Demanding6–8 h
  4. Hardmore than 8 h

Demanding

  • Longest day · stage 48 h

Climate

Days in season · lowest point
20–30°C
Nights in season · highest point
1–7°C
Wet days a month
4–10
Daylight
11.0–15.2h
SeasonDay high and night low−20 °C−10 °C0 °C10 °C20 °C30 °C40 °CWet days, at the highest point51015Daylight9.4 h10.5 h11.8 h13.3 h14.5 h15.2 h14.9 h13.9 h12.4 h11.0 h9.7 h9.1 hJanFebMarAprMayJunJulAugSepOctNovDec
Climate by month, 1995–2024 average
MonthLowest point, day high / night low (°C)Highest point, day high / night low (°C)Wet daysSnow daysFrost nights at the highest pointDaylight (h)
January10.9 / 4.8-2.5 / -8.29.99.1319.4
February11.6 / 4.4-1.9 / -8.38.97.928.210.5
March13.9 / 5.90.3 / -6.610.39.130.811.8
April16.8 / 8.33 / -4.210.67.828.213.3
May21.3 / 12.27.1 / -0.19.8416.414.5
June26.4 / 16.611.8 / 4.36.40.62.415.2
July29.9 / 19.514.9 / 73.70014.9
August29.8 / 19.914.8 / 7.25.50013.9
September24.6 / 16.510.3 / 3.58.90.42.412.4
October20.4 / 13.36.9 / 0.69.7312.311
November15 / 9.11.6 / -413.310.627.59.7
December11.9 / 6-1.5 / -711.59.930.99.1

Climate by month

Averages for 1995–2024 from ERA5 reanalysis via Open-Meteo, at the trail's lowest and highest point, adjusted to each point's elevation. Bars span the mean night low to the mean day high; wet days have at least 1 mm of rain, snow days at least 1 cm of snow. Daylight runs from sunrise to sunset in the middle of the month. The shaded months are the trail's season.

Stages

RouteDistanceAscentDescentElevationTime
1Calenzana Ortu di u Piobbu11.3 km1,430 m ↑160 m ↓280 → 1,550 m6 h 30
2Ortu di u Piobbu Carrozzu7.3 km690 m ↑950 m ↓1,550 → 1,290 m7 h 00
3Carrozzu Ascu Stagnu4.9 km820 m ↑650 m ↓1,270 → 1,450 m6 h 10
4Ascu Stagnu Tighjettu8.4 km1,200 m ↑960 m ↓1,420 → 1,670 m8 h 00
5Tighjettu Ciottulu di i Mori6.4 km690 m ↑350 m ↓1,650 → 1,990 m4 h 00
6Ciottulu di i Mori Manganu25.0 km820 m ↑1,210 m ↓2,000 → 1,600 m8 h 00
7Manganu Petra Piana8.4 km840 m ↑570 m ↓1,610 → 1,880 m6 h 30
8Petra Piana L'Onda9.9 km500 m ↑930 m ↓1,850 → 1,420 m4 h 50
9L'Onda Vizzavona10.1 km660 m ↑1,170 m ↓1,450 → 950 m6 h 05
10Vizzavona E Capannelle14.1 km1,050 m ↑410 m ↓970 → 1,600 m5 h 15
11E Capannelle Prati17.6 km1,050 m ↑830 m ↓1,600 → 1,810 m6 h 10
12Prati Usciolu10.9 km730 m ↑810 m ↓1,810 → 1,740 m5 h 45
13Usciolu Cuscionu (Matalza)10.8 km330 m ↑680 m ↓1,750 → 1,410 m4 h 25
14Cuscionu (Matalza) Asinau9.9 km650 m ↑500 m ↓1,410 → 1,560 m4 h 15
15Asinau Paliri15.3 km600 m ↑1,090 m ↓1,540 → 1,050 m7 h 00
16Paliri Conca13.2 km360 m ↑1,160 m ↓1,050 → 250 m5 h 00

Totals and averages count the main stages only. Distances are ours, measured on the OpenStreetMap map line between the stage ends: no source publishes them. Walking times from Parc naturel régional de Corse. ≈ marks our estimates where the source gives no figure: ascent and descent and heights from the terrain model (Copernicus DEM, 30 m grid, sampled every 100 m), to the nearest 10 m.

Terrain

Highest · lowest point
2,595m high251m low

Gradient

The steepest 500 m of the trail in walking direction, uphill and downhill. On this trail the steepest climb is 46 % (25°, 232 m up over 500 m) on stage 4, the steepest descent −50 % (27°, 249 m down) on stage 2.

A gradient is height per distance: 20 % means 20 m up for every 100 m forward. Percent and degrees don't grow alike: 100 % is 45°, not 90°.

GradientAngleFeels like
10 %6°Noticeable on a road
20 %11°A steep path, slow going
30 %17°Very steep, often steps
100 %45°Scrambling

Averages over 500 m from a 30 m terrain model: short pitches within them, such as steps and ladders, are steeper.

46% ↑−50% ↓

Steep stretches

How many kilometres of the main route climb or descend at 15 % or more (9°, 15 m of height per 100 m), measured in 200 m stretches: on this trail 31.7 km up and 30.4 km down, the darkest parts of the profile. Such stretches are slow going uphill and hard on the knees downhill.

62.1km

Surfaces

  • Natural ground: 96%, 171.3 km. Earth, grass, rock and roots: footpaths and forest trails. Can be muddy after rain.
  • Gravel: 3%, 5.5 km. Gravel, compacted and stony surfaces: mostly forest roads and farm tracks.
  • Paved: 1%, 1.2 km. Asphalt, concrete and cobbles: roads and village streets.

96% natural3% gravel1% paved
600 m1,000 m1,400 m1,800 m2,200 m2,600 mTree line 1,750–1,800 m2,595 m12345Stage 6789Stage 10Stage 11121314Stage 15Stage 160 km178 km

Terrain along the route

Heights from the Copernicus terrain model (30 m grid, every 100 m along the main route); it measures the treetops in forests, so heights may differ from signposts by some metres.

The profile colours each 200 m by its gradient in walking direction: the steeper, the darker, climbs warm and descents violet, from level ground to ±30 % and beyond.

The strip under the profile shows the ground underfoot, from OpenStreetMap; for the 78% of the route without a surface tag, the type of way decides (footpaths natural, tracks gravel).

The tree line marks the height where trees stop growing in this region, between 1,750 and 1,800 m depending on the slope (Wikipédia (fr)). Above it the route crosses open ground without trees. Pasture and clearing can keep the forest lower than this in places.

Landscape

Forest39%Grassland and shrubs58%Bare rock and sand3%Farmland and villages1%12345Stage 6789101112131415160 km178 km

Landscape along the route

Land cover from ESA WorldCover 2021 (10 m satellite map), every 100 m along the main route; each point takes the most common class within 30 m, so the path itself doesn't count as bare ground. Its eleven classes are folded into the six groups shown. It says what the landscape looks like, not which plants grow there.

Sleeping

Wild camping is prohibited. Tents only beside the refuges; pitching along the trail is not permitted.

14.6 km without a bedCamping26Huts28Hostels6Rooms312345Stage 6789101112131415160 km178 km

Places to sleep along the route

One tick per place to sleep along the main route, from OpenStreetMap: 26 campsites, 28 huts, 6 hostels, 3 guest houses within 1 km of the trail or 3 km of a stage's end (stage towns often lie off the trail). Hotels and day shelters are left out. The shaded column is the longest stretch without any, from km 150.7 to 165.3. The map may miss places or list ones that have closed, so book or check locally.

Water & Supply

Clean water

41 fountains, taps and springs marked as drinkable in OpenStreetMap within 500 m of the trail, and 4 places to sleep OpenStreetMap marks as having drinking water. Clean water also counts the 54 huts, hostels, guest houses and campsites within 500 m where hikers usually fill a bottle: guests come first, and many close out of season, so ask, and carry a little more than the gaps need. Places OpenStreetMap marks as without drinking water are left out. The counts include the approach and variant; the chart shows the main route.

Rated by the longest stretch of the main route without clean water: frequent up to 10 km, regular up to 20 km, scarce beyond. Here: from km 0.3 to 11, stage 1.

10.7kmRegular

Any water

Clean water, and the 47 springs within 500 m of the trail whose water is of unknown quality: filter, boil or treat it, and expect some springs to run dry in late summer. Here the longest stretch without any water runs from km 45.5 to 54.3. Rated like clean water: frequent up to 10 km, regular up to 20 km, scarce beyond.

8.8kmFrequent

Shops

11 supermarkets, convenience and general stores and petrol stations with a shop in OpenStreetMap, within 1 km of the trail or 3 km of a stage's end (stage towns often lie off the trail). Small village shops are often missing, and opening hours vary: check before relying on one. Here the longest stretch without runs from km 91.3 to 130.6.

39.3km
Water · 8.8 km withoutPublic drinking water · 18.3 km withoutSprings (treat before drinking) · 13.1 km withoutRefills at places to sleep · 14.6 km withoutShops · 39.3 km withoutSupermarkets · 178 km withoutConvenience and general stores · 41.5 km withoutPetrol station shops · 91.3 km without12345Stage 6789Stage 10Stage 11121314Stage 15160 km178 km

Water and shops along the route

One tick per place along the main route, from OpenStreetMap: drinking water and springs within 500 m, refills at huts, hostels, guest houses and campsites within 500 m, shops within 1 km or 3 km of a stage's end. The shaded band in each lane is its longest stretch without; "Water" counts every kind, and opens into one lane per kind, each with its own. The map may miss places or list ones that have closed or run dry, so check locally.