The isalo is the jewel of the National 7. A ruiniform massif, work of nature by the erosion of the tenderest soils to see outcrops the hardest.

The Isalo National Park offers sumptuous landscapes and is crossed by deep canyons several kilometres long. The vegetation found there is rupicolous and endemic as aloes, pachypodiums, kalanchoe and also many medicinal plants. In the middle of a particularly dry landscape, natural pools sometimes appear, like oases.