Isalo is a massif of ochre sandstone in the dry south of Madagascar, cut into canyons, spires and flat-topped domes, and from the road it looks like nothing but desert. The rock is why that is wrong. Isalo's sandstone is porous: it takes up the rare rains like a sponge and lets the water out again, slowly, as springs deep in the canyons. So your walk starts across open plateau of grass and bare rock with no shade at all. Then it drops through a gap in the wall into shade, water and trees. The canyon floor is damp, a stream runs under pandanus palms, and the temperature changes as you go down. Ring-tailed lemurs come to the water, and white Verreaux's sifakas leap from trunk to trunk overhead.
Up on the plateau the trails run among wind-cut spires and flat-topped domes, walked early because the bare rock gives no shade. Thirteen of the plants up here grow on this massif and no other, among them the elephant's foot, which keeps its own water in a swollen trunk. The cliffs hold the dead as well. The Bara bury in two stages. A body is left in a low cave for some months, then the bones are carried up and sealed into niches high in the sandstone, the hardest to reach the most honourable. These are graves still in use, not ruins, so you look from the canyon floor, where the piled stones and zebu skulls on the ledges are clear enough. South of Ranohira a natural window in the rock, the Fenêtre de l'Isalo, takes the sun at the end of the day, and the massif holds its red for only a few minutes. The rock's own water is saved for the middle of the walk. The Piscine Naturelle is a clear pool ringed by palms at the foot of the walls, fed by a spring in the rock, cold enough to shock you after a morning on bare rock.