GR 20 Grande Randonnée #20 (or Great Walk in English) is a long distance trail that traverses Corsica diagonally from north to south. It is considered to be the most difficult of all the GR routes and one of the most beautiful mountain trails in Europe. It is approximately 180km long with variation in height of about 3,000 metres and can be walked in 12 to 15 days. Even though the GR20 doesn't require any climbing experience it is very demanding and is often very exposed, perfect fitness level and confidence in mountaineering over a variety of rugged terrains is necessary.
We chose the GR20 after reading an article in a climbing magazine, the GR20 was listed as a top 10 Hikes in the world.
A few sites for more information and references: