This park was established in 1962 and covers 81,540 hectares of a wildly eroded sandstone massif. The grassy plains are surrounded by sandstone ridges sculpted into wild forms, and secluded in the rocks are many Sakalava Tombs. The Canyon des Singes ('Canyon of Monkeys') makes for an interesting day walk, and you'll have a good chance of seeing sifakas (a common lemur) leaping through the trees. A local guide is required for visitors entering the park, and guides and porters can be hired in Ranohira. Treks in the park can last from several hours to a week or longer.
The animals of the Isalo are typical of the climate and the vegetation. 77 species of birds live in Isalo among which the Benson rock-thrush Pseudocossyphus bensoni, an endemic species of Madagascar. There are14 species of nocturnal lemurs, 8 of which are introduced and seven endemic to Madagascar.
You can also walk along the canyon to the Piscine Naturelle - a hot and thirsty walk but worth it for the breathtaking landscape along the way. The Grotte des Portugais is at the northern end of the park. The cave isn't worth seeing, but the surrounding Forêt de Sahanafa is beautiful, with natural springs and a lot of lemurs.
The Isalo is about 400km south-west of Tana, and the nearest town is Ranohira.