Arguably one of the hardest long-distance hikes in Europe, the GR 20 takes backcountry travel to a whole new level. The trail crosses Corsica end to end, and has very few miles of travel without some sort of technically challenging terrain. Refugios, or mountain huts, along the way provide some food, which helps save on pack weight. Exposure is one of the cruxes of this trail, with some sections featuring narrow tread and steep drop-offs. Expect plenty of rock scrambling, chain climbing, loose scree, steep climbs and descents, and questionable weather.
Despite the difficult terrain, the trail is well marked and blazed, and there is a plethora of information available online. Water is plentiful along the route, but be sure to fill up whenever you see a source. Late into summer, some water sources might not be readily available. The trail is loosely defined, and involves a lot of picking your way around obstacles and along challenging segments, looking for the next blaze or cairn. You can reserve spots at the refugios, and it is recommended you do so during the most popular hiking season.