Iguazú Falls is a line of 275 waterfalls along nearly three kilometres of cliff on the border of Argentina and Brazil, set in rainforest, and at its centre the river collapses into an eighty-two-metre chasm called the Devil's Throat. Nothing about it is a single drop. The cliff is a staircase of old lava, so the water comes down in steps and in dozens of separate falls, with green islands and forest between them. On the Argentine side a long catwalk runs out over the upper river, flat and quiet, until it ends at a railing where the water goes over the edge and the noise takes over. From there the Devil's Throat is a horseshoe of white with its floor hidden in spray. Small dark birds cross it: great dusky swifts nest on the wet rock behind the curtain, and every one of them flies through the falling water to get home.
Iguazú is two parks, and each side gives what the other cannot. Argentina puts you inside the falls: the Lower Circuit brings you almost level with the foot of several of them, close enough for the spray to drift over the railing and for a rainbow to hang in it on a sunny morning. Boats leave from below the falls and push upriver until the pilot noses straight into the base of Salto San Martín; the engine vanishes under the noise, the white wall closes overhead, and you come out soaked. Brazil gives you the whole line at once: a paved trail along the top of the far gorge stays with the falls for their full width, with the Devil's Throat filling the view at the end. Away from the boardwalks, the Macuco trail runs three and a half kilometres through closed forest, one of the last pieces of the Atlantic Forest that once ran the length of Brazil's coast. The Guaraní say a serpent god tore the river open here to drown a girl who had fled him with a mortal lover, and Iguazú still looks like something torn open rather than worn down.