GR20

The GR 20 is a GR footpath that crosses the Mediterranean island of Corsica running approximately north–south, described by the outdoor writer Paddy Dillon as "one of the top trails in the world".

The whole trail is about 180 km long with 12,000 m of elevation gain, and is clearly waymarked throughout. Every year, approximately 10,000 to 20,000 hikers walk along the trail, typically completing it in about 15 days. The trail is considered to be the most difficult of all the GR routes and consists of two parts: the northern part, between Calenzana and Vizzavona and the southern part, between Vizzavona and Conca.

Source: Wikipedia