Fish River Canyon is the largest canyon in Africa — about 160 kilometres long, up to 27 kilometres from rim to rim, and close to 550 metres deep. The river it is named after did only the last part of the work. The gorge started as a break in the crust: faults tore open more than 500 million years ago and a block of ground dropped between them, and around 300 million years ago glaciers ground their way along that trough. Only afterwards, as the rim of the continent lifted when Gondwana came apart, did the Fish River begin sawing the narrow inner canyon into the hard, dark basement rock you can still pick out at the very bottom. The view from the top is that whole sequence stacked in order — pale benches of sandstone, terrace under terrace, then the sudden slot where the water runs.
Stand at the main viewpoint above Hobas and what strikes you is the silence: no sound of water comes up, because for most of the year there is barely any. The Fish River runs only intermittently, flooding in late summer and then shrinking to a chain of long, still pools strung along the floor. Those pools are what make the canyon walkable. Between 1 May and 15 September — the only window permits are issued, because summer down there hits the high forties — hikers in groups of at least three climb down at Hikers' Viewpoint and follow some 85 kilometres of sand, boulder and river crossing for four or five days, with no road, no shop and no easy way out, finishing at the hot springs of ǀAi-ǀAis. Everyone else stays on the rim, where quiver trees grow straight out of the rubble and raise yellow flower spikes in the middle of winter.