A mountain range rising from the sea, Corsica holds the most arrestingly beautiful landscapes in the Mediterranean. From its cobalt blue gulfs and shell-sand beaches, hillsides of evergreen maquis give way to pristine oak, chestnut and pine forests, awesome gorges, alpine lakes and a spine of snow-streaked peaks and passes. Among the many trails that penetrate its remotest corners, the GR20, following the island's watershed, is a high-level route that has won an international reputation as being Europe's most challenging long-distance path.