The Tarn is a secondary river of the french Garonne, whose source is located in the Massif Central near the Mont lozère, and which joins the Garonne at Castelsarrasin.
The most famous part of this river is the "Gorges du Tarn", a 50km long portion located in its upper part in the mountains, from Sainte Enimie to Millau (near the famous newly built "Viaduc of Millau", Europe's biggest).
The Gorges du Tarn are located between two "Causses" (the local name for the wide plateaux of the region), the "Causse Méjean" and the "Causse de Sauveterre". These highlands of this part of the Massif Central are made of gentle limestone, where the water has made its way, eroding these deep gorges.
The Gorges du Tarn are not the only gorges of this kind in the area, there are also the Gorges de la Dourbie, which join the Tarn in Millau, and the Gorges de la Jonte, which join the Tarn in Le Rosier, in the Tarn's gorges themselves.
All of these locations form a very beautiful region, not very famous abroad, but very touristic amongts french people, especially those of the region.
There are superb rafting/kayak/canoe descents to be done on these rivers, and superb world-famous rockclimbing spots.
Some picturesque roman villages are nestled inside the gorges, such as Peyreleau, Le Rosier, Saint Marcellin, Les Vignes, La Croze, La Malène, Saint-Chély, Hauterive, Castelbouc, La Caze, Sainte Enimie. In some places like the cirque of Saint Marcellin, can be observed houses in the cliffs themselves.