Then, about two-and-a-half hours into our hike, in the mossy wall of the Aqueduct, I saw this:
The flower was only about a centimeter across.
At home my books yielded nothing, except a pink and suggestively-named Disa vaginata. After Googling it for a better view, though, I came up with a thread on an orchid forum that yielded results: Disa glandulosa.
* I say 'climbing' because on Skeleton Gorge one has to climb some ladders and scramble over boulders in the almost-vertical kloof bed. That's the fun part. Up to that point it's just a steady, uphill, huffing and puffing (for me) slog. Many more pictures to come.