The Tarn gorges run for about 50 kilometres north and west from near Florac, cut 500 metres deep into the limestone of the Causses. The canyon road (D907bis) follows the river the whole way, with viewpoints, cliff villages, and access points for kayaks and swimmers. Le Rozier and La Malène are the main bases; Saint-Chély-du-Tarn is one of the prettiest villages along the route.
You can drive it in a couple of hours, kayak the gentler middle section in a day, or hike the cliff paths above for a much harder full picture. Best between May and September; the river is too cold and the road quieter in winter.