The 175km/109mi-long Verdon flows from the peaks of the Mercantour to the Durance, crossing the limestone plateaux of the Prealps through a 700m/2,297ft-deep canyon. It wasn't until 1905, when the gorges were explored by the founder of potholing (Martel), that impressive viewing points and roads were created. Its turquoise water attracts canoe-kayak enthusiasts, while the GR4 trail, known as the "Blanc-Martel" will lead you into the heart of the Grand Canyon.